engleski

RNA Pol II promotes transcription of centromeric satellite DNA in beetles

Transcripts of centromeric satellite DNAs are known to play a role in heterochromatin formation as well as in establishment of the kinetochore. However, little is known about basic mechanisms of satellite DNA expression within constitutive heterochromatin and its regulation. Here we present comprehensive analysis of transcription of abundant pericentromeric satellite DNAs from beetles (Coleoptera), PRAT from Palorus ratzeburgii and TCAST from Tribolium castaneum. Both satellites are expressed in all three developmental stages: larvae, pupae and adults at similar level. Transcripts are abundant and are heterogeneous in size ranging from 0.5 kb up to more than 5 kb. Transcription proceeds from both strands but with 10 fold different expression intensity and transcripts are not processed into siRNAs. Most of the transcripts (80%) are not polyadenylated and remain in the nucleus while a small portion is exported to the cytoplasm. Multiple, irregularly distributed transcription initiation sites as well as termination sites have been mapped within the PRAT and TCAST sequences using primer extension and RLM-RACE. The presence of cap structure as well as poly(A) tails in a portion of the transcripts indicate RNA polymerase II – dependent transcription and a putative polymerase II promoter sites were mapped by computational approach. The treatment with alpha-amanitin decreases the level of transcripts at concentrations that selectively inhibit pol II activity. In conclusion, stable, RNA polymerase II dependant transcripts of abundant centromeric satellite DNAs, not regulated by RNAi, have been identified and characterized. There is strong indication that both satellite DNAs are transcribed as autonomous transcription units from own promoters that reside within satellite sequences. Transcripts remain in the nucleus and are proposed to play a structural role in the organization of pericentromeric heterochromatin.

satellite DNA; transcription; centromere

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