P31, a mammalian housekeeping protein encoded by a multigene family containing a high proportion of pseudogenes

The primary structure of P31, a 13.300 kDa mammalian 'housekeeping' protein, was deduced from the nucleotide sequence of a rat recombinant cDNA clone. The P31 mRNA has 950 nucleotides and codes for a protein of 121 amino acids. This mRNA is present in several mouse tissues and in other mammals. Nuclei of rapidly growing cells contain mature P31 mRNA and a distinctive set of larger transcripts. P31 is encoded by a multigene family. Five members of the family were isolated from a mouse genomic library and restriction mapping and S1 nuclease analysis of four of them (P31-4, P31-12, P31-13 and P31-14) suggest that they are processed genes. The very low homology of the fifth (P31-8) with respect to the corresponding cDNA sequence indicates that it is a pseudogene. Although the features of the mRNA and the genes encoding P31 exhibit extensive similarity with those of ribosomal proteins, neither the identity nor the biological function of the protein has yet been determined.