Nucleic Acids Research, 2000, Vol. 28, No. 17 3346-3353
© 2000 Oxford University Press
Levels of free PABP are limited by newly polyadenylated mRNA in early Spisula embryogenesis
Department of Biochemistry, University of Cambridge, 80 Tennis Court Road, Cambridge CB2 1GA, UK and 1Departimento de Biologia Celular, Universidade de Brasilia, 70910-900 Brasilia DF, Brazil
The poly(A) tail of eukaryotic mRNAs regulates translation and RNA stability through an association with the poly(A)-binding protein (PABP). The role of PABP in selective polyadenylation/deadenylation and translational recruitment/repression of maternal mRNAs that occurs in early development is not fully understood. Here, we report studies including UV-crosslinking and immunoblotting assays to characterise PABP in the early developmental stages of the clam Spisula solidissima. A single, 70 kDa PABP, whose sequence is highly homologous to vertebrate, yeast and plant PABPs, is detected in oocytes. The levels of clam PABP are constant in early embryogenesis, although its ability to crosslink labelled poly(A) is ‘masked’ shortly after fertilisation and remains so until the larval stage. Full RNA-binding potential of PABP in embryo lysates was achieved by brief denaturation with guanidinium hydrochloride followed by dilution for binding and crosslinking or by controlled treatment of lysates with Ca2+-dependent micrococcal nuclease. Masking of PABP, which accompanies cytoplasmic polyadenylation in maturing oocytes and in in vitro activated oocyte lysates, is very likely due to an association with mRNAs that bear new PABP target binding sites and thus prevent protein binding to the labelled A-rich probe. Functional implications of these findings as well as the potential application of this unmasking method to other RNA-binding proteins is discussed.
* To whom correspondence should be addressed. Tel: +44 1223 333673; Fax: +44 1223 766002; Email: nms@mole.bio.cam.ac.uk Present addresses: Osvaldo P. de Melo Neto, Centro de Pesquisas Aggeu Magalhes, FIOCRUZ, Campus da UFPE, Av. Moraes Rego s/n Caixa Postal 7472, 50670-420 Recife PE, Brazil James A. Walker, Department of Genetics, Howard Hughes Medical Institute, Duke University, Durham, NC 27710, USA
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