title: Cloning in a cosmid vector of complete 37 kb and 25 kb ribosomal DNA repeat units from the chicken.
abstract: DNA fragments of up to 40 kb containing rRNA-coding sequences have been isolated from a chicken liver DNA library prepared in the cosmid pHC79. Characterization of the cloned DNA by R-loop and restriction mapping has shown that there are two size classes of repeat unit, one of 37 kb and one of 25 kb, the larger of which is a family of units which vary slightly in size. These two classes were shown to be present in the DNA of a single chicken. The size of the internal transcribed spacer in the chicken was measured to be 4.4 kb from analysis of R-loops and heteroduplexes between chicken and Xenopus laevis rDNAs. No introns were observed in either the 18 S or the 28 S coding sequences. The number of copies of the chicken rDNA unit was measured by titration against the cloned sequences to be 202 +/- 51 per haploid genome.
mesh_terms: D000818:Animals; D001482:Base Composition; D002645:Chickens; D003001:Cloning, Molecular; D004247:DNA / Q000378:metabolism*; D004262:DNA Restriction Enzymes; D004275:DNA, Ribosomal; D008099:Liver / Q000378:metabolism; D009690:Nucleic Acid Conformation; D010957:Plasmids; D012335:RNA, Ribosomal / Q000235:genetics; D012091:Repetitive Sequences, Nucleic Acid
chemical_list: D004275:DNA, Ribosomal; D012335:RNA, Ribosomal; D004247:DNA; D004262:DNA Restriction Enzymes