The suffix sequence is involved in processing the 3' ends of different mRNAs in Drosophila melanogaster

We describe here the nucleotide sequences of several genomic and mRNA copies of the suffix, a short dispersed actively transcribed repeat located at the 3' ends of many different genes of Drosophila melanogaster. Only one strand of the suffix is transcribed. The patterns of suffix-containing mRNAs vary during development. The five randomly selected genomic copies of the suffix are 265 bp long and quite conservative in their sequence. The non-transcribed strand is terminated with oligo(A) preceded by AATAAA sequence. No repetitive flanking sequences can be detected. The three other genomic copies selected by hybridization with suffix-containing cDNA clones are less conservative, especially in the 5' part. In particular, they contain short insertions carrying a polyadenylation signal AATAAA at exactly the same position of the suffix. Comparison of genomic and cDNA clones shows that mRNAs are polyadenylated at the last nucleotide of these insertions. The cDNA clones include the same part of the suffix, from the 39th to 112th nucleotide. Thus, a segment of the suffix forms the last exon for both genes. In one case, the beginning of the last intron coincides with the beginning of suffix, creating a very unusual donor splicing site. We conclude that the suffix sequence is directly involved in the formation of the last splicing site and 3'-end maturation of mRNA, at least in the case of the two genes analysed.