Formins: phosphoprotein isoforms encoded by the mouse limb deformity locus.

Mutations at the mouse limb deformity (ld) locus result in defects of growth and patterning of the limb and kidney during embryonic development. The gene responsible for this phenotype is large and complex, with the capacity to generate a number of alternatively spliced messenger RNA transcripts encoding nuclear protein isoforms called "formins." We have made polyclonal antibodies to specific formin peptides and have confirmed the authenticity of the antibodies' reactivity, using cell lines derived from mice with molecularly defined mutations at the ld locus. In addition, we have used these antibodies to detect and characterize polypeptides encoded by both wild-type and mutant ld alleles. In so doing, we show that a formin isoform (i) is modified by posttranslational phosphorylation at serine and threonine residues and (ii) when present in a crude nuclear extract, is retained by DNA-cellulose.