mRNA precursor splicing in vivo: sequence requirements determined by deletion analysis of an intervening sequence

To define the extent of intervening sequence required for splicing higher eukaryotic mRNA precursors in vivo, we constructed deletions within the second intervening sequence of the human G gamma-globin gene that progressively approach the donor or acceptor splice sites. Most of the intervening sequence can be deleted with no effect on splicing. At the donor splice site, 6 bases of intervening sequence are sufficient for accurate and efficient splicing. At the acceptor splice site, 20 bases are sufficient for accurate and efficient splicing, and 16 bases are sufficient for accurate splicing but at a reduced level. However, 15 bases are insufficient for splicing at a significant level. The effect of deletions ending near the acceptor splice site is independent of whether an A-G dinucleotide is introduced into the acceptor splice site region by the deletion.