Cloning and characterization of two processed pseudogenes and the cDNA for the murine U1 snRNP-specific protein C

• Published in: Gene 1997-01, Vol.184 (2), p.273-278
• Main Authors: Nelissen, Rob L.H, Klein Gunnewiek, Jacqueline M.T, Lambermon, Mark H.L, Van Venrooij, Walther J
• Format: Article
• Language: English
• Subjects: Animals; Cloning, Molecular; DNA, Complementary; Evolution; Evolution, Molecular; Genomic library; Humans; Mice; Molecular Sequence Data; Mouse; Multigene Family; Peptides - genetics; Pseudogene; Pseudogenes; Ribonucleoprotein, U1 Small Nuclear - metabolism; Ribonucleoproteins, Small Nuclear - genetics; Ribonucleoproteins, Small Nuclear - metabolism; Sequence Homology, Amino Acid; Substrate Specificity; U1-C; Xenopus Proteins
• ISSN: 0378-1119; 1879-0038
• DOI: 10.1016/S0378-1119(96)00612-9

Genes for the snRNP proteins U1-70K, U1-A, Sm-B′/B, Sm-D1 and Sm-E have been isolated from various metazoan species. The genes for Sm-D1 and Sm-E, which were isolated from a murine and human source respectively, appear to belong to a multigene family. It has been suggested that also for the mammalian U1-C protein such a multigene family exists. With the human U1-C cDNA as a probe, two genes containing sequences homologous to the probe sequence were isolated from a mouse genomic library. Simultaneously, a murine U1-C cDNA was isolated from a mouse cDNA library. This 0.74 kb cDNA contains an open reading frame (ORF) of 477 bp encoding a polypeptide of 159 amino acids (aa) which differs at only one position (position 65) from the human U1-C protein. One of the isolated U1-C genes contains an ORF as well and shares 92% nucleotide sequence identity with the mouse U1-C cDNA. The features of this gene, in particular the absence of introns, the acquisition of a 3′ poly(A) tail and flanking direct repeats, indicate that it represents a processed pseudogene. At the predicted aa sequence level, substitutions of conserved residues at functionally important positions are observed, strongly suggesting that expression of this gene would not lead to a functional polypeptide. The second U1-C gene appeared to be a pseudogene as well because it is also intronless and contains a frameshift mutation compared to the ORF in the mouse U1-C cDNA. The characterization of these two pseudogenes points to the existence of a U1-C multigene family in mice. Furthermore, comparison of aa sequences of the murine, human and Xenopus U1-C shows that the protein is highly conserved through evolution. Since the Xenopus U1-C differs from the two mammalian counterparts solely at a number of positions in the C-terminal region, it can be concluded that aa changes are less well tolerated in the N-terminal region of U1-C than in the rest of the protein.