FORMINS - PHOSPHOPROTEIN ISOFORMS ENCODED BY THE MOUSE LIMB DEFORMITYLOCUS

Mutations at the mouse limb deformity (ld) locus result in defects of growth and patterning of the limb and kidney during embryonic developm ent. The gene responsible for this phenotype is large and complex, wit h 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 ha ve confirmed the authenticity of the antibodies' reactivity, using cel l lines derived from mice with molecularly defined mutations at the ld locus. In addition, we have used these antibodies to detect and chara cterize polypeptides encoded by both wild-type and mutant ld alleles. In so doing, we show that a formin isoform (i) is modified by posttran slational phosphorylation at serine and threonine residues and (ii) wh en present in a crude nuclear extract, is retained by DNA-cellulose.