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Flory, P. J., and Fox, T. G (1951), J . Am. Chem. SOC. 73, 1904. Flory, P. J., and Leonard, Jr., W. J. (1965), J . Am. Chem. SOC.87, 2102. Flory, P. J., and Miller, W. G . (1966), J. Mol. Biol. IS, 298. Glick, R . E., Stewart, W. E., and Mandelkern, L. (1966), Biochim. Biophys. Acta 120, 302. Hanlon, S. (1966), Biochemistry 5, 2049. Hanlon, S., and Klotz, I. M. (1965), Biochemistry 4, 37. Mandelkern, L. (1964), Crystallization of Polymers, New York, N. Y . , McGraw-Hill. Markley, J. L., Meadows, D. H., and Jardetky, 0. (1967), J . Mol. Bio!. 27, 25. Miller, W. G., Brant, D. A., and Flory, P. J. (1967),
J . Mol. Biol. 23, 67. Nagai, K. (1961), J . Chem. Phys. 34, 887. Oya, M., Kuno, K., and Iwakura, Y . (1966), Kogyo Kagaku Zashi 69, 741. Quadrifoglio, F., and Urry, D. W. (1967), J. Phys. Chem. 71, 2364. Stake, M. A., and Klotz, I. M. (1966), Biochemistry 5, 1726. Stewart, W. E., Mandelkern, L., and Glick, R. E. (1967a), Biochemistry 6, 143, Stewart, W. E., Mandelkern, L., and Glick, R. E. (1967b), Biochemistry 6, 150. Teramoto, A., Nakagawa, K., and Fujita, H. (1967), J. Chem. Phys. 46, 4197. Yu, H., and Stockmayer, W. H. (1967), J . Chem. Phys. 47, 1369.
Variations in Leucine Transfer Ribonucleic Acid in Mouse Plasma Cell Tumors Producing K -Type Immunoglobin Light Chains * J. Frederic Mushinski and Michael Potter
ABSTRACT: A comparison was made of the chromatographic profiles of leucyl transfer ribonucleic acid from normal mouse liver and from several murine plasma cell tumors all of which secrete a unique example of the same antigenic class ( K ) of immunoglobulin light chain. Using the Freon-Aliquat 336 reversed-phase column at least five leucyl transfer ribonucleic acid peaks are seen in profiles from liver and several tumors, with stable, reproducible differences among them in the relative proportion of each isoaccepting species. Certain
M
ultiplicity of tRNAs has been established in bacteria and higher organisms (Doctor et al., 1961; Weiss and Kelmers, 1967; Caskey et al., 1968; Yang and Novelli, 1968a). In only a few cases so far has a correspondence been shown between the several isoaccepting tRNAs and the multiple codons for an amino acid (Weisblum et al., 1962; von Ehrenstein and Dais, 1963; Kano-Sueoka et al., 1968; Caskey et al., 1968). Compared with a system having only a single translational equivalent (codon and adaptor) for each amino acid the existence of several code words and multiple tRNAs for a single amino acid could permit additional versatility in protein synthesis. Evolution has not diminished this degeneracy and, instead, may have
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* From the Laboratory of Biology, National Cancer Institute, Bethesda, Maryland 20014. Receiced Nocember 5, 1968.
MUSHINSKI AND POTTER
other tumors producing the same class of light-chain protein appear to be very deficient in peaks 3 and/or 5 suggesting that these tumors do not have significant amounts of these components normally found in mammalian transfer ribonucleic acid. It is suggested that these quantitative and qualitative variations in leucyl transfer ribonucleic acid within a very closely related group of similarly differentiated tissues indicate that the different leucyl transfer ribonucleic acid genes are under independent control.
found some special values and uses for alternate codonanticodon combinations specifying a single amino acid in regulating processes in more complex higher organisms such as mammals. Manipulation of this degenerate adaptor system may play a role in differentiation of complex genomes (Holland et al., 1967) or in regulation of intracellular protein synthesis (KanoSueoka and Sueoka, 1966; von Ehrenstein, 1966). It has been speculated that a flexible, but regulated, translational system for immunoglobulin molecules could, with genetic economy, greatly increase the number and variability of immunoglobulins an organism could generate (Potter et al., 1965; Campbell, 1967; Mach et al., 1967). Owing to the greater complexity in higher organisms, we would not consider the translational machinery of a whole organism as is usually done in yeast or bacteria, but we have the opportunity to look at individual tissues
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from this point of view. For example, we can compare the tRNA of a highly specialized mammalian tissue with that of a n organ such as the liver whose synthetic capabilities and other biological functions are many and complex. As a model tissue to which differentiation has conferred a more restricted function we selected that small group of mineral oil induced mouse plasma cell tumors which secrete an excess of the light chain portion of immunoglobulin molecules. These tumors are examples of specialized tissues which are nearly identical in many respects including the genetically inbred nature of the host mouse strain (BALBlc), the morphologic tissue type (plasma cell neoplasm) and the protein secretory product (K-type light chains). With so many similarities, any differences found in the translational machinery may be related to that detail in which all these tumors differ from one another, the amino acid sequence of the protein product. The light chains secreted by several of the tumors selected for study have been studied chemically (Hood et ai., 1966) and have been used as raw material for the generation of theories of immunoglobulin variation. Thus, this system has clear advantages for correlating translational events with end products of protein synthesis because these products are well characterized and vary not in class of protein but only in certain amino acid residues. We investigated the tRNA portion of the translational apparatus, not forgetting that there are many alterations made on tRNA molecules which might be responsible for the appearance of chromatographic differences, and that decoding properties of tRNA owe much of the specificity to the aminoacylating enzymes. Since leucine has a large number of code words assigned to it (Marshall et al., 1967) and, presumably, anticodon-containing adaptor molecules, our efforts were directed toward separating the mammalian tRNA species specific for this amino acid. Countercurrent distribution appears to offer the most powerful separatory potential for tRNA subspecies (Weisblum et ai., 1965), though its use with mammalian Leu-tRNA has not been reported. Reversed-phase column chromatography is another powerful means of fractionating these tRNAs and has been successful with mammalian preparations (Weiss and Kelmers, 1967; Yang and Novelli, 1968a). Moreover, this type of fractionation permits direct comparison between two different tRNA preparations distinguishable by charging with amino acids bearing different radioactive labels and then fractionating the aminoacyl-tRNA. In Escherichia coli six code words have been assigned to leucine; in this report we have demonstrated at least five components in mammalian Leu-tRNA. Comparison of the chromatographic profiles of the Leu-tRNA prepared from light-chain-secreting tumors reveals reproducible patterns for each tumor with certain qualitative and quantitative differences among them. Materials and Methods Plasma Cell Tumors. Mineral oil (MOPC) and adjuvant-induced (Adj. PC) plasma cell tumors were
I4 n
I
I
I1
I
VOLUME 1ml.l
1: Chromatographic pattern of 1 M NaCI-0.001 M MgCl2 extracts of total ethanol precipitate following phenol extraction of MOPC 315 tumors; 203 A260 units in 3.5 ml was applied to a 1 X 36 in. column of Sephadex G-100 equilibrated with 1 M NaCI-0.001 M MgClz and eluted at 4" with this same buffer at a rate of about 10 ml/hr. Four peaks of material absorbing light at 260 mp were routinely recovered and named, as indicated, I A , IB, 11, and 111. Peak IB frequently merges with peak I A or I1 if excessive material or excessive volume is applied to the column. FIGURE
maintained by continuous transplantation in BALBjc mice as described elsewhere (Potter, 1966). RNA Preparations. Tumors were harvested from mice before extensive necrosis occurred. The animals were killed by cervical dislocation, and the tumor nodules were removed, trimmed of necrotic tissue, and plunged immediately into preweighed beakers of ice-cold medium E (0.01 M Tris-HC1 (pH 7 . 3 , 0.001 M MgC12, and 0.0001 M Na2EDTA). The initial medium E was decanted from the pooled, weighed tumors which were then placed in a chilled Waring Blendor with 1.5 volumes (v/w) of medium E plus 10 mglml of bentonite. After a preliminary 5-sec homogenization, an equal volume of redistilled phenol which had been saturated with distilled water or medium E was immediately added and homogenization continued for 2 min. The phenol mixture was transferred to a plastic bottle and shaken a t room temperature for 30 min. After centrifugation for 10 min at 13,OOOg in a refrigerated centrifuge, the aqueous layer was aspirated and kept in ice. The phenol layer was reextracted by shaking with one-half the original volume of medium E for 30 min at room temperature followed by centrifugation and aspiration of aqueous phase. The pooled aqueous phases were reextracted with 50-ml portions of aqueous phenol two or three times. The RNA was precipitated at -20" by the addition of 0.1 volume of 20y0 potassium acetate (pH 5.5) and 2.5 volumes of absolute ethanol. After standing at -20" overnight, the precipitate was collected by centrifugation, drained free of ethanol in the cold, and extracted in the cold sequentially with three 10-ml portions of 1 M NaCl0.001 M MgC12. About 450 , 4 2 6 0 units of RNA in less than 10 ml of NaCI-MgC12 extract was introduced onto a G-100 Sephadex column (1 X 36 in.) and
LEUCINE
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Sephadex G-100 Fractionation of 203 A200 Units of 1 M NaC1-0.001 Tumor (see Figure 1).
TABLE I:
Recovery
M
MgClz Extract from MOPC 315
After Water Dialysis
Vol (ml)
A260
A280
A260
A280
A260
units
units
units
Vol (ml)
A260
Fraction
units
units
units
Lyophilized Dry Wt (mg)
[14C]Leu Acceptance" (ppmoles/A2~0unit)
IA IB I1 I11
83 59 117 121
0.630 0.219 0.460 0.327
0.330 0.097 0.220 0.169
52.3 12.9 53.8 39.6
115 94 152 182
0.435 0.113 0.321 0.039
0.249 0.064 0.170 0.024
50.0 10.6 48.8 7.1
3.9
