J. Biol. Chem., Vol. 265, Issue 1, 34-39, Jan, 1990
A single base exchange in an intron of the Dictyostelium discoideum alpha-actinin gene inhibits correct splicing of the RNA but allows transport to the cytoplasm and translation
W Witke and AA Noegel
Max-Planck-Institut fur Biochemie, Martinsried, Federal Republic of Germany.
The genomic structure of the alpha-actinin gene from Dictyostelium
discoideum has been determined. The coding region consists of three exons
separated by two short introns located at either end of the gene. In an
alpha-actinin mutant, HG1130, about 1% of alpha-actinin protein products
are found compared to the parent strain AX2. The size of the mutant
proteins are 88 and 95 kDa. In HG1130, the second intron is improperly
spliced from the primary alpha-actinin transcript resulting from a mutation
at the 5' splice site from a GT to an AT. The premature RNA is less
efficiently cleaved at the mutated 5' splice site and the following step of
the splicing reaction, ligation of exons 2 and 3, is prevented. Thus, two
RNA species are generated, one in which intron 2 is not removed and one in
which exon 2 is not ligated to exon 3. The two RNA species are stable,
transported to the cytoplasm, bound to polysomes and translated. In vitro
and in vivo, the partially spliced RNAs are translated into proteins of 88
and 95 kDa which can be immunoprecipitated with an alpha-actinin-specific
monoclonal antibody. The in vivo stability of the mutant proteins is
comparable to the wild type alpha-actinin.
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