Identification of a Balb/c Mouse Proα1(I) Procollagen Gene: Evidence for Insertions or Deletions in Gene Coding Sequences

Abstract

We report the first isolation and identification of a mouse genomic fragment encoding amino acid sequences for the pro alpha 1(I) chain of type I procollagen. The DNA sequence of eight coding sequences is presented; five of these are 54 bp and three are 108 bp in length. Together these specify 198 amino acids which are 94% homologous to the corresponding bovine pro alpha 1(I) chain protein sequences. Each of the eight coding sequences is flanked by appropriate splice-junction sequences that exhibit considerable sequence complementarity to the rat small nuclear U1a RNA. In the 198 codons examined in this mouse genomic clone, the preferred codons for glycine and alanine are GGU (46/67) and GCU (23/30), respectively. This is in contrast to the codon usage reported for the chicken pro alpha 1(I) cDNA clone (Fuller and Boedtker, 1981). The examined coding sequences exhibit considerable nucleotide homology in both end-to-end and in staggered alignments. Based on an analysis of this homology data, a model is presented for the generation of 108-bp coding sequences from 54-bp units by two successive homologous recombinational events within coding sequences. Alternatively, the 108-bp units may have arisen by precise deletions of an intervening sequence between 54-bp coding sequences. Evidence supporting this is provided by a comparison of pro alpha 1(I) and pro alpha 2(I) genes. In the mouse pro alpha 1(I) gene amino acids 856-891 are encoded in a 108-bp unit; the chicken pro alpha 2(I) gene these residues are encoded in two 54-bp coding sequences. In addition, the coding sequences for nearly 50% of the alpha domain are condensed in the pro alpha 1(I) gene into a region approximately one half the size occupied by the comparable sequences in the pro alpha 2(I) gene.

DNA sequence analysis of a mouse pro alpha 1 (I) procollagen gene: evidence for a mouse B1 element within the gene.

“…As a prerequisite to studies of developmental gene regulation, considerable attention is being focused on the structures of the genes encoding the constituent polypeptide (proa) chains of type I procollagen. In particular, these are the proa2(I) genes from chickens (54,55) and sheep (45) and the proal(I) gene from mice (39). The proa2(I) genes are the largest, most highly interrupted genes yet identified in eucaryotes.…”

“…The preponderance of 54-base-pair (bp) coding sequences observed in this gene led to the hypothesis that procollagen genes arose by the amplification of a primordial 54-bp unit (55). However, a more compact genomic organization is observed in a proal(I) procollagen gene (39). Therefore, a more complex evolutionary history, involving successive unequal cross overs within coding sequences (CSs) or precise deletions or insertions of intervening sequences or both, has been postulated for procollagen genes (39).…”

“…However, a more compact genomic organization is observed in a proal(I) procollagen gene (39). Therefore, a more complex evolutionary history, involving successive unequal cross overs within coding sequences (CSs) or precise deletions or insertions of intervening sequences or both, has been postulated for procollagen genes (39).…”

“…The isolation of the mouse proal (I) gene segment analyzed in this paper has been described previously (39). The DNA sequence of the inserts from two subclones, pMPClC and pMPClA, was established essentially by the protocol of Maxam and Gilbert (38).…”

“…fractionated by agarose gel electrophoresis, and transferred to nitrocellulose by the Southern procedure (47) after partial depurination (51). The KpnI-BamHI subfragment of MPC1A was "P labeled with radioactive dCTP in a T4 DNA polymerase reaction (39). Hybridizations were performed in 50% formamide-5xSSC-50 mM Tris-hydrochloride (pH 7.4)-i mM EDTA-0.1% sodium dodecyl sulfate-lOx Denhardt solution (13) for 18 h at 37°C.…”