Avvedimento VE, Acquaviva AM, Varrone S. Repetitive and non-repetitive sequences in the transcript in vitro of porcine thyroid chromatin.
EUROPEAN JOURNAL OF BIOCHEMISTRY 1977;
78:1-10. [PMID:
913390 DOI:
10.1111/j.1432-1033.1977.tb11707.x]
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Abstract
Purified pig thyroid chromatin has been transcribed in vitro with Escherichia coli RNA polymerase. The transcript, analyzed by DNA-RNA hybridization, shows two major kinetic components: 40% of the transcript is copied by repetitive sequences present 100 times per haploid genome; another 25% anneals to DNA with a rate constant Kh 10-4 M - S-1, typical of single-copy sequences. The transcript annealed at cot = 40 M - S to fractions of 2000-nucleotide DNA, when banded in neutral CsCl gradient only hybridizes to the heavy side of the main band. At cot = 3000 M - S, another hybridizing fraction appears on the light side of the main band of the gradient. The reassociation properties of these fractions show that the heavy DNA fraction is reiterated about 100 times per haploid genome, whereas the light DNA appears as a unique sequence, associated to small repetitive elements. The transcript, analyzed by formamide/sucrose gradient, shows two peaks with sedimentation coefficients of 10 S and 4 S, respectively. The 10-S RNA, hybridized to native 2000-nucleotide-length DNA, has a Kh of 10-4 M - S-1 and a cot1/2 of 10(3) M - S, typical of single-copy sequences.
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