C4SR, a novel zinc-finger protein with SR-repeats, is expressed during early development of Xenopus

The protein C4SR contains two cysteine(4) (C-4) zinc-finger motifs at its a mino terminus, a stretch of acidic residues in the middle and a series of s erine-arginine (SR) repeats at its carboxyl terminus. A cDNA clone encoding the zinc-finger domain was first selected from a Xenopus laevis oocyte exp ression library on the basis of the ability of the fusion protein to stably bind an RNA probe. The mRNA encoding C4SR is expressed during oogenesis, a nd the protein is present at a constant level in oocytes and early embryos. The C4SR protein is expressed in transcriptionally active erythroblasts bu t not in transcriptionally inert mature erythrocytes. An epitope-tagged C4S R protein, expressed in oocytes, associates with nascent transcripts at man y loci in lampbrush chromosomes and is absent from storage particles (snurp osomes) containing the normally recognized complement of RNA splicing compo nents. It is likely that C4SR is involved in pre-mRNA transcription/packagi ng rather than in exon Splicing. The zinc-finger motif, present as two copi es in C4SR, is also present in a range of transcription-associated proteins . We suggest the descriptor (DW)C-4, in which DW refers to the invariant as partic acid (D)/tryptophan (W) dipeptide that precedes the first cysteine r esidue, for this distinctive zinc-finger structure. (C) 2000 Elsevier Scien ce B.V. All rights reserved.