A repetitive structure in the chick alpha 2-collagen gene.
Explore the source record for details and available documents.
Animals↗
Biomedical subjects
M Mudryj
Publications and source records attributed to M Mudryj.
The collagen gene: evidence for its evolutinary assembly by amplification of a DNA segment containing an exon of 54 bp.
We have determined the size and sequence of 8 exons in the gene that specifies chick type 1 alpha 2 collagen. These 8 exons represent three different segments of the gene, but all encode information for the helical portion of the protein. Seven exons have a length of 54 bp, and the 8th has a size of 99 bp. The sequences within these exons vary except for th glycine codons, which occur every third triplet. Each exon begins with a glycine codon and ends with a triplet that precedes a glycine codon. The size and the sequences of the introns do not show any homology except at their ends. Of 7 introns examined the first six bases at the 5' end of 5 of these are identical. The sequences at the 3' end of the introns also show homologies. Our results imply that the ancestral gene for collagen arose by multiple duplications of a single genetic unit containing a 54 bp condig segment. The sequences within these exons drifted by successive point mutations and in some cases by additions or deletions of 9 bp or multiples of 9 bp.
Animals↗
Isolation and characterization of overlapping genomic clones covering the chicken alpha 2 (type I) collagen gene.
A series of overlapping recombinant clones, which cover the alpha 2 (type I) collagen gene, have been isolated by stepwise screening of two libraries of chicken genomic DNA fragments. The first genomic clone was isolated by using a cloned cDNA containing alpha 2 collagen DNA sequences as hybridization probe. The other clones were obtained by a sequence of screenings using defined fragments of the successive genomic clones as hybridization probes. Several types of experiments indicated that the DNA of these clones are truly overlapping and span 55 kilobase pairs of contiguous DNA sequences in the chicken genome. Sequence analysis of small DNA segments of some of these clones confirm that they contain coding sequences which specify alpha 2 collagen. Electron microscopic analysis of hybrids between type I alpha 2 collagen mRNA and the overlapping genomic clones indicates that the chicken alpha 2 collagen gene has a length of at least 37 kilobases, about 7.4 times longer than the corresponding translatable cytoplasmic mRNA. The coding information for alpha 2 collagen is distributed in more than 50 coding sequences which are interrupted by intervening sequences of various sizes. The structure of the gene implies that the conversion of precursor RNA to mature mRNA for alpha 2 collagen includes at least 50 splicing events.
Animals↗
Nitrous acid mutagenesis of duplex DNA as a three-component system.
Purified native Hemophilus influenzae DNA is relatively insusceptible to nitrous acid (NA) mutagenesis in vitro, but is readily mutated following denaturation. NA mutagenicity for duplex DNA is significantly increased in the presence of various alcohols, glycols, phenols or primary amines. Phenol-extracted DNA contains dissociable contaminants of low molecular weight that enhance NA mutagenesis. Enhancement of NA mutagenesis by phenol and by spermine is due to the formation of unstable molecular species. We propose that reactive organic nitroso compounds are formed which then serve as delivery vehicles to promote mutagenicity of native DNA, perhaps via transnitrosation reactions. Similar reactions probably occur in vivo to promote NA-induced base substitution (but not frameshift) mutations in Salmonella typhimurium and in Escherichia coli. The possible significance of these observations to carcinogenesis is discussed.
DNA, Bacterial↗
Specificity of the bacteriophage lambda N gene product (pN): nut sequences are necessary and sufficient for antitermination by pN.
We have cloned the nutR site together with the tR1 site of bacteriophage lambda in the E. coli galactose operon to examine whether the lambda promoter sequences PR and PL are involved in the recognition specificity of the lambda N gene product (pN). We first constructed a derivative of plasmid pBR322 in which the expression of the tetracycline genes (tet) is controlled by the gal promoter (Pgal). This new plasmid contains a unique Hind III site between Pgal and tet into which the nutR and tR1 sites were introduced. The order of the relevant genetic markers in this second plasmid is Pgal-nutR-tR1-tet. Cells transformed with this plasmid express tet only if pN is provided and if the plasmid contains an intact gal promoter. Our data suggest that transcription which originates at Pgal is modified by pN at nutR, enabling it to pass through tR1 into tet. We conclude that promoters do not play a specific role in pN recognition and that nut sequences are both necessary and sufficient for pN action.
Bacteriophage lambda↗
Conservation of the sizes for one but not another class of exons in two chick collagen genes.
Type III collagen is often found in the same tissues as type I collagen, yet the function and nature of the fibrils formed by the two collagens differ markedly. To understand the evolutionary history of the collagen gene family in more detail, we isolated the gene for type III collagen and compared its structure with that of the gene for alpha 2(I) collagen. This comparison points to a remarkable conservation in the size distribution of the exons coding for the helical part of these two collagen polypeptides: equivalent amino acid segments in the helical domain of each polypeptide are encoded by exons of equal sizes in each gene. This suggests that after the interstitial collagen genes had been duplicated from a common ancestor about 2-5 X 10(8) years ago, no recombinations between these exons were tolerated, although the same recombinational phenomena must have played an important part in shaping the structure of the progenitor for these genes. This fixation of the size distribution of the exons which code for the interstitial collagen helical domains is found despite the persistence in these exons of sequence elements that should have favoured recombinational rearrangements, and contrasts with the variations in the pattern of sizes of some exons coding for the amino and carboxyl propeptides of these collagens.
Amino Acid Sequence↗