Four murine c-abl mRNAs arise by usage of two transcriptional promoters and alternative splicing.

The c-abl gene in mice is transcribed into two major and at least two minor mRNAs which have different 5'-ends, but are otherwise colinear. Here we show that the two major mRNAs are initiated by separate promoters and that the minor transcripts arise by alternative splicing. Like in the human gene, one of the alternative murine 5' c-abl exons lies far upstream of the remaining exons. The major mRNA that begins with this exon has about 1275 nucleotides upstream of the abl coding region. Interestingly, this unusually long upstream mRNA segment contains multiple short open reading frames both in mouse and man and is highly conserved in sequence between these species. The 5'-most c-abl promoter contains several sequence motifs that are highly conserved between mouse and man. The downstream promoter is much less conserved.