Modulation of differential transcription of tRNA genes through chromatin organization

Parthasarthy, Akhila and Gopinathan, Karumathil P (2005) Modulation of differential transcription of tRNA genes through chromatin organization. In: Biochemical Journal, 391 . pp. 371-381.

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Abstract

In higher eukaryotes, tRNA multigene families comprise several copies encoding the same tRNA isoacceptor species. Of the 11 copies of a $tRNA_{1}^{Gly}$ family from the mulberry silk worm Bombyx mori, individual members are differentially transcribed in vivo in the B. mori-derived BmN cell lines and in vitro in silk gland nuclear extracts. These genes have identical coding regions and hence harbour identical internal control sequences (the A and B boxes), but differ significantly in their 5' and 3' flanking regions. In the present study, we demonstrate the role of chromatin structure in the down-regulation of the poorly expressed copy, $tRNA_{1}^{Gly}$-6,7. Distinct footprints in the 5'-upstream region of the poorly transcribed gene in vitro as well as in vivo suggested the presence of nucleosomes. A theoretical analysis of the immediate upstream sequence of this gene copy also revealed a high propensity of nucleosome formation. The low transcription of $tRNA_{1}^{Gly}$-6,7 DNA was further impaired on assembly into chromatin and this inhibition was relieved by externally supplemented TFIlIC with an associated histone acetyltransferase activity. The inhibition due to nucleosome assembly was absent when the 5'-upstream region beyond -53 nt was deleted or entirely swapped with the 5'-upstream region of the highly transcribed gene copy, which does not position a nucleosome.Foot printing of the in vitro assembled $tRNA_{1}^{Gly}$-6,7 chromatin confirmed the presence of a nucleosome in the immediate upstream region potentially masking TFIIIB binding. Addition of TFIIIC unmasked the footprints present on account of the nucleosome. Our studies provide the first evidence for nucleosomal repression leading to differential expression of individual members from within a tRNA multigene family.

Item Type:	Journal Article
Publication:	Biochemical Journal
Publisher:	Portland Press Ltd
Additional Information:	Copyright for this article belongs to Portland Press Ltd.
Keywords:	Bombyx mori;chromatin immunoprecipitation (ChIP) assay;chromatin organization;modulation;nucleosome assembly; transcription of tRNA genes
Department/Centre:	Division of Biological Sciences > Microbiology & Cell Biology
Date Deposited:	13 Dec 2005
Last Modified:	19 Sep 2010 04:22
URI:	http://eprints.iisc.ac.in/id/eprint/4471

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