THE PRIMARY STRUCTURES OF RAT RIBOSOMAL-PROTEINS S3A (THE V-FOS TRANSFORMATION EFFECTOR) AND OF S3B

The amino acid sequence of the rat 40S ribosomal subunit protein S3a w as deduced from the sequence of nucleotides in two recombinant cDNAs a nd confirmed by the determination of the NH2-terminal sequence by Edma n degradation. Ribosomal protein S3a has 263 amino acids (the NH2-term inal methionine is removed after translation of the mRNA) and the mole cular weight is 29,794. The protein designated S3b has the same amino acid sequence as S3a except that it lacks the carboxyl-terminal 12 res idues. We are unable to determine whether there are separate genes for S3a and S3b, or whether there is a single gene and alternate splicing of the precursor to yield separate mRNAs for S3a and S3b, or whether there is a single gene and a single mRNA whose translation yields S3a which is converted by proteolysis, either physiological or fortuitous, to S3b. The mRNA for S3a is about 1000 nucleotides in length. Hybridi zation of cDNA to digests of nuclear DNA suggests that there are 8-13 copies of the S3a gene. Rat ribosomal protein S3a is identical to the product of the rat Fte-1 gene which encodes the V-Fos transformation e ffector; S3a is also related to the plant protein cyc07, which is enco ded by a cell cycle S-phase specific gene. (C) 1996 Academic Press, In c.