LOCALIZATION OF SACCHAROMYCES-CEREVISIAE RIBOSOMAL-PROTEIN L16 ON THESURFACE OF 60-S RIBOSOMAL-SUBUNITS BY IMMUNOELECTRON MICROSCOPY

Antibodies raised against a trpE-L16 fusion protein expressed in Esche richia coli were used to examine immunological relatedness between Sac charomyces cerevisiae ribosomal protein L16 and ribosomal proteins fro m eubacteria, halobacteria, methanogens, eocytes, and other eukaryotes . Homologues of L16 also were identified by searches of sequence data bases. Among the bacterial proteins that are immunologically related a nd similar in sequence to L16 are ribosomal proteins that bind 5 S rRN A. L16 protein fused near its carboxyl terminus to E. coli beta-galact osidase could assemble into functional yeast 60 S ribosomal subunits. The RPL16AlacZ gene fusion partially complemented the slow growth or l ethality of mutants containing null alleles of one or both RPL16 genes , respectively. L16-beta-galactosidase fusion protein cosedimented wit h ribosomes and polyribosomes, and remained associated with high salt- washed ribosomes. Monoclonal antibodies against beta-galactosidase wer e used to map the location of L16-beta P-galactosidase on the surface of the 60 S subunit by immunoelectron microscopy. L16 was localized ne ar the top surface of the central protuberance, where the 60 S subunit potentially contacts the 40 S subunit. This is similar to the locatio n of the bacterial homologues of L16 in 50 S ribosomal subunits.