Cloning and characterization of two processed pseudogenes and the cDNA for the murine U1 snRNP-specific protein C.
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.
Nelissen
R L
RL
Department of Biochemistry, University of Nijmegen, The Netherlands.
Gunnewiek
J M
JM
Lambermon
M H
MH
Van Venrooij
W J
WJ
D000818:Animals; D003001:Cloning, Molecular; D018076:DNA, Complementary; D019143:Evolution, Molecular; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D005810:Multigene Family; D010455:Peptides / Q000235:genetics; D011544:Pseudogenes; D017412:Ribonucleoprotein, U1 Small Nuclear / Q000378:metabolism*; D017411:Ribonucleoproteins, Small Nuclear / Q000235:genetics* / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity; D029867:Xenopus Proteins
D018076:DNA, Complementary; D010455:Peptides; C491261:RNP-C protein, Xenopus; D017412:Ribonucleoprotein, U1 Small Nuclear; D017411:Ribonucleoproteins, Small Nuclear; C491260:SNRPC protein, human; C104347:Snrp1c protein, mouse; D029867:Xenopus Proteins