STRUCTURE OF THE DROSOPHILA DNA TOPOISOMERASE-I GENE AND EXPRESSION OF MESSAGES WITH DIFFERENT LENGTHS IN THE 3' UNTRANSLATED REGION

The nucleotide sequence of the Drosophila DNA topoisomerase I gene (to p1) has been determined. Structurally, top1 consists of eight exons an d seven introns. The top1 coding region contains a new class of opa re peats, encoding clusters of serine residues instead of glutamine repea ts usually seen in Drosophila genes of the neurogenic loci. A unique f eature of top1 is the developmental switch of its transcripts: a heter ogeneous population of transcripts ranging from 3.8 to 4.2kb seen maxi mally at 0-2 h of embryogenesis and a 5.2-kb transcript maximal at 6-1 2 h of embryonic development. The transcripts expressed in the 0-2-h e mbryo have been shown as maternal storage products specific to ovarian tissues. RACE analysis shows that whereas the 6-12-h transcripts have a single site for polyadenylation, there are at least 12 different si tes for poly(A) addition to the 0-2-h transcripts. An additional intro n specific for the maternal storage transcripts appears in some of the 0-2-h transcripts. No significant heterogeneity at the 5' end of the top1 transcripts is seen. Sequence searches have revealed a number of regulatory sequences for potential translational control in the 3' unt ranslated region. (C) 1998 Elsevier Science B.V. All rights reserved.