[
Nature,
1988]
For myosin to function properly in muscle, its bipolar filaments must be assembled in ordered arrays. A major problem facing cell biologists is the control of local assembly of the filaments. Within non-muscle cells, the filaments are continually assembling and disassembling according to local signals. In muscle cells, however, myosin must be turning over continuously within a permanent array and, therefore, the cells must be replacing myosin subunits or whole filaments in an organized fashion. Two different approaches have now been applied to find out how this is achieved. The first is a classical genetic approach in which mutants of the nematode worm Caenorhabditis elegans with incorrect myosin assembly are isolated; and the second is by inducing expression of portions of the myosin molecule in bacteria. The differences in the information about myosin filament assembly provided by these two methods offer a nice contrast between genetic and molecular-biology approaches to a cell biology problem. Analysis of mutants reveals behaviours requiring molecular explanations, whereas the expression of pieces of the molecule gives information