Summary of Significant Findings of the PL 480

Project 01-062-1 "Physiological Role of Bacterial Ribonucleases"

RNases I and III of Salmonella typhimurium have been purified to
homogeneous states and RNase II has been extensively purified. Using
the different affinities of the RNases for ribosomes, a single step
procedure for separation of RNases I, II and III has been developed. A
method for preparation of ribosomes without ultracentrifugation has
also been developed. RNase I minus mutant of S. typhimurium has been
isolated by nitrosoguanidine treatment.

RNase I specifically associates with 30s ribosomal subunit (3 molecules
of enzyme per 30s subunit). Me?* dependent inhibition of RNase I by 30s
and 70s ribosomes is lost by differential salt treatments of 70s ribosomes
and restored by reconstitution of ribosomal particles with detached
proteins. Unlike 70s ribosomes and 30s subunits, 50s subunits of
Escherichia coli and S. typhimurium are attacked by RNase I whereas
Lactobacillus plantarum ribosomes (even 70s) are attacked by the enzyme.
The importance of ribosomal configuration is emphasized by the observation
that Streptomycin protects E. coli 70s ribosomes and 30s subunits against

. +
the attack of RNase I at low Me" concentrations.