Microtubule-associated proteins (MAPs): a monoclonal antibody to MAP 1 decorates microtubules in vitro but stains stress fibers and not microtubules in vivo.

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Abstract
A monoclonal antibody (mAb 7-1.1) was produced against a bovine brain microtubule-associated protein (MAP) preparation that was separated from tubulin after initial purification by cycles of microtubule assembly and disassembly in vitro. The antibody reacted specifically with 2 high MW polypeptide of the MAP 1 class, designated MAP 1.1 and MAP 1.2, and also with the surfaces of MAP 1-containing microtubules that was assembled in vitro. Double immunofluorescence microscopy using mAb 7-1.1 and a well-characterized rabbit anti-tubulin antibody revealed that mAb 7-1.1 stained stress fibers in fixed and permeabilized cultured mammalian cells rather than microtubules. The antibody also stained cell nuclei in a punctate fashion. mAb 7-1.1 is one of a number of monoclonal antibodies that react with presumptive MAP 1 polypeptides. Some of the MAP 1 antibodies were found to bind specifically to microtubules in fixed and permeabilized cells, while other were reported to react with nonmicrotubule structures. The results, together with the results of other investigations, indicate that MAP 1 may be a family of several high MW polypeptides that adventitiously behave as MAP by the criterion of in vitro coassembly with tubulin through cycles of polymerization and depolarization but whose cellular distributions, and perhaps functions, are varied.