The Drosophila Hrb98DE Locus Encodes Four Protein Isoforms Homologous to the A1 Protein of Mammalian Heterogeneous Nuclear Ribonucleoprotein Complexes

Abstract

The Drosophila Hrb98DE locus encodes proteins that are highly homologous to the mammalian Al protein, a major component of heterogeneous nuclear ribonucleoprotein (RNP) particles. The Hrb98DE locus is transcribed throughout development, with the highest transcript levels found in ovaries, early embryos, and pupae. Eight different transcripts are produced by the use of combinations of alternative promoters, exons, and splice acceptor sites; the various species are not all equally abundant. The 3'-most exon is unusual in that it is completely noncoding. These transcripts can potentially generate four protein isoforms that differ in their N-terminal 16 to 21 amino acids but are identical in the remainder of the protein, including the RNP consensus motif domain and the glycine-rich domain characteristic of the mammalian Al protein. We suggest that these sequence differences could affect the affinities of the proteins for RNA or other protein components of heterogeneous nuclear RNP complexes, leading to differences in function.