4380
B 1O C H E M I S T R Y
DLNN AND WONG
Structure and Stability of the Reconstituted Intermediate Particles Involved in the in Vitro Self-Assembly of the 30s Ribosomal Subunit? John M. Dunn and Kin-Ping Wong*si
ABSTRACT: In an attempt to decipher further the molecular mechanism of the self-assembly of the 30s ribosomal subunit, we have studied the hydrodynamic properties, conformation, and stability of the major reconstitution intermediate, RI, and its heat-activated form, RI*. Preliminary hydrodynamic parameters (flf,,,or Reff)of R I are similar to those of the 30s particle, while those for RI* are similar to those of the 1 6 s RNA. This indicates that, during the course of the 3 0 s assembly, the hydrodynamic shape and/or compactness of 16s R N A appear to switch back and forth as the 1 6 s R N A proceeds through the RI, then the RI*, and finally the 3 0 s subunit. The melting of the 16s RNA, RI*, and 3 0 s subunit was studied simultaneously by three different conformational parameters, and all show complex behavior through the whole temperature range studied (25-90 "C). The RI* is similar to the 1 6 s R N A at low temperature (
