Another difference: Its ultraviolet absorption pattern is temperature-de pendent between 20 c and 60° C. T w o stranded DNA's U V pattern is not. Other differences include:
RESEARCH
• Its weight-average molecular weight decreases upon enzyme deg radation according to a function ex pected for a single-stranded m o l e c u l e different from a function for a twostranded molecule. • It reacts with formaldehyde at 37° C. a n d is precipitated by P b + + ions. This shows that t h e purine and pyrimidine rings a r e not tied u p in a hydrogen-bonded, complementary structure b u t are available for reaction. • It does not have a complementary nucleotide composition. Adenine and thymine contents a n d guanine and cytosine contents are not equal.
MAKING ADJUSTMENTS. Robert L. Sinsheimer, who h a s isolated a n d identified a single-stranded D N A molecule, makes adjustments o n t h e ultracentrifuge. T h e Caltech biophysieist u^es the instrument to separate and characterize D N A
Single-Strand DNA Found Caltech scientist isolates a D N A molecule which does not fit the n o w - a c c e p t e d theory o f D N A structure A . BIOPHYSICIST at California
Institute
of Technology has found w h a t appears to he a single-stranded D N A (deoxy ribonucleic a c i d ) . Though t h e genetic implications of the finding a r e still in doubt, it may lead eventually to a better understanding of many nucleic acid properties, including h o w R N A (ribonucleic acid) replicates. All previous samples of D N A which have been characterized have h a d m o lecular contents u p around 120 million or more and molecular weights of 6 to 12 million. They have fitted the b e havior patterns predicted for a twostrand chain held together by hydrogen bonding and wound in a helix. Robert L. Sinsheimer, the Caltech scientist, found this single-stranded D N A while searching for a low-molecular weight 40
C&EN
JUNE
I,
1959
DXA with which to study biological activity as a function of chemical struc ture of the D N A molecule. H e chose a DNA from the φΧ174 virus, which has a particle weight of about 6.2 million and a DNA molecular weight of 1.7 mil lion—about one fourth to one fifth t h e molecular weight of DNA's previously studied. Sinsheimer noticed early in his iso lation of t h e φΧ D N A that it did n o t act as t h e usual D N A does. It h a d several differences: First, its radius of gyration ( a measure of molecular size) is smaller than predicted for twostranded D N A of t h e same molecular weight. Also, its radius of gyration is a function of ionic strength of the so lution. Two-stranded DNA's radius of gyration is not.
The simplest explanation for all these observations, Sinsheimer says, is that φΧ DNA is a single-stranded molecule. How important this finding is is hard to assess at this stage of t h e game, how ever. This is because w e still d o not Icnow how a single-stranded D N A rep licates—that is, whether it replicates by a mechanism different from that of its two-stranded cousins or whether t h e basic mechanism is t h e same. Sinsheimer's programs include trying to determine this. H e also plans to continue his study of structure vs. activity of the φΧ D N A . Furthermore, he feels that the molecule is small enough so that he can eventually un ravel its structure. This work has been supported by a grant from the American Cancer So ciety and will b e published soon in t h e maiden issue of JOUVTIQI of Aîolcculo.>" Physics.
New Cardenolide Seen Researchers at Georgetown University, Washington, D . C , have partially synthesized a 2'-deoxy cardenolide—a compound which m a y prove to b e an important chemical for treating heart ailments. T h e compound is a monodigitoxoside of digitoxigenin, an extract of the naturally occurring digitalis, which is used as a cardiac stimulant. The compound also may play a n important role in pinpointing t h e structure of t h e naturally occurring compound. Georgetown chemists \V. W e r n e r
NEW BLOCKSON CATALOG
Just
clip
coupon
If you buy phosphates ot any chemical listed below, here is your basic reference data in handy pocket size. Properties, uses, etc. concisely presented for quick reading. Catalog i n cludes many time-saving tables and charts, M A I L THE COUPON.
or ad to your
business
letterhead 1
I I 1 I
Blockson Chemical Company Division of Olin Mathieson Chemical Corp. Joliet, Illinois Send the New Blockson Catalog.
ZONE
BLOCKSON CHEMICAL COMPANY Joliet,
Illinois
/ Division
of Olin Mathieson
Chemical
Corporation *«-
G o W
Sodium Tripolypfiosphate · Tetrasodium Pyrophosphate · Trisodium Phosphate (Crystalline-Monohydrate) · Trisodium Phosphate Chlorinated · D i sodium Phosphate (Crystalline-Anhydrous) · Monosodium Phosphate (Anhydrous-Monohydrate) · Sodium Polyphos (Sodium HexametaphosphateSodium Tetrapbosphiate) · Sodium Acid Pyrophosphate · Tetrapotassium Pyrophosphate · Sodium Fluoride · Sodium Silico-Fluoride · C-29 Sequestering Agent · Teox t20(Nonionic Surfactant) · Hydrofluoric Acid · Sulfuric Acid. JUNE
I,
1959 C&EN
4 1
THINKING OF
RESEARCH
CHEMISTRY?
THINK OF MAUMEE ! ! Μ Λ Ι Ι Ι
Λ Τ Τ Λ
§*t r-k
