CLONING, EXPRESSION, AND PROPERTIES OF THE MICROTUBULE-STABILIZING PROTEIN STOP

Nerve cells contain abundant subpopulations of cold-stable microtubule s. We have previously isolated a calmodulin-regulated brain protein, S TOP (stable tubule-only polypeptide), which reconstitutes microtubule cold stability when added to cold-labile microtubules in vitro, We hav e now cloned cDNA encoding STOP, We find that STOP is a 100.5-kDa prot ein with no homology to known proteins, The primary structure of STOP includes two distinct domains of repeated motifs, The central region o f STOP contains 5 tandem repeats of 46 amino acids, 4 with 98% homolog y to the consensus sequence, The STOP C terminus contains 28 imperfect repeats of an 11-amino acid motif, STOP also contains a putative SH3- binding motif close to its N terminus, In vitro translated STOP binds to both microtubules and Ca2+-calmodulin. When STOP cDNA is expressed in cells that lack cold-stable microtubules, STOP associates with micr otubules at 37 degrees C, and stabilizes microtubule networks, inducin g cold stability, nocodazole resistance, and tubulin detyrosination on microtubules in transfected cells, We conclude that STOP must play an important role in the generation of microtubule cold stability and in the control of microtubule dynamics in brain.