MOLECULAR CHARACTERIZATION OF A NOVEL RAT PROTEIN STRUCTURALLY RELATED TO POLY(A) BINDING-PROTEINS AND THE 70K PROTEIN OF THE U1 SMALL NUCLEAR RIBONUCLEOPROTEIN PARTICLE (SNRNP)

A cDNA has been isolated from a rat testis library which encodes a novel protein of 100 kDa that contains domains found in two different proteins involved in the processing of pre-mRNAs. Computer-assisted comparison reveals that one sequence motif of 30 amino-acid residues is very similar to a region conserved in the C-terminal part of eukaryotic poly(A) binding proteins (PABP). A second region of the rat 100 kDa protein, containing alternating basic, mostly arginine, and acidic amino-acid residues, is structurally related to sequence motifs found in the 70K protein of the U1 small nuclear ribonucleoprotein particle (snRNP), which is involved in RNA splicing. Northern blot analysis shows that a corresponding 9.5 kb transcript is highly expressed in rat testis; lower mRNA levels are found in other tissues such as liver, kidney, lung and brain. Ontogenic studies reveal that the expression of the 100 kDa protein-encoding gene and sexual maturation are correlated, being barely detectable during early post-natal life but reaching maximal levels around the first month after birth.