This project deals with the genetic and biochemical analysis of bacterial mutants unable to assemble ribosome subunits at low temperature. Among such mutants we have found several groups in which the genetic lesions map outside the str-spc region of the chromosome, and which map away from each other. Since we developed an in vitro assay for the maturation of the incomplete ribosome units, we will use this assay to purify the factor(s) responsible for the apparent in vitro maturation, and to monitor the trimming of precursor S23 RNA. The principal properties of the factor(s) will be studied, along with the mode of its activity. Such mutants may be altered in factors that participate in the assembly process, but which are not structural components of the ribosome. Bibliographic references: Sypherd, P., and S. Osawa. Ribosome Genetics Revealed by Hybrid Bacteria in Ribosomes, (ED) Nomura, Tissieres and Lengyel, 1974. Paznokas, J. and P. Sypherd. 1975. Respiratory capacity, 3',5'-cyclic Adenosine monophosphate and morphegenosis of Mucor racemosus. J. Bacteriol. 123.