Transcription of repetitive sequences on Xenopus lampbrush chromosomes.

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Abstract
The lampbrush chromosomes of X. laevis were reinvestigated and found suitable for the study of transcription by in situ hybridization to nascent RNA transcripts. The transcription of 3 repetitive sequences that do not show any sequence homology and that differ in their degree of interspersion was analyzed. They are located on different parts of the chromosomes: 2 are clustered, 1 is interpersed. All 3 of these sequences are transcribed at the lampbrush chromosome stage and transcripts from both strands of each sequence can be detected. The amount of transcription is apparently not proportional to the number of copies of the repetitive sequence at a given chromosomal locus, suggesting that other sequences are involved in the regulation of their transcription.