Centriole Duplication: Centrin in on

ody has been characterized in detail [6], the vast majority of the proteins that make up centrioles and centrosomes remain unknown. There are a few families of proteins known to localize to spindle pole bodies and to centrosomes, but most of them are involved in microtubule nucleation at the periphery of these structures and not as architectural components [7,8]. Genetic and biochemical approaches will eventually fill in the details of centriole structure and function, but for now details are few. Centrins are one of the relatively few proteins known to localize to centrioles [9]. They are small, calciumbinding proteins belonging to the calmodulin superfamily. Centrins have attracted interest, not least because they are a rare example of a centriolar protein with a known homolog in the yeast spindle pole body, in this case Cdc31p. Cdc31p localizes to a substructure of the spindle pole body called the `half-bridge' [10], and temperature-sensitive yeast mutants in Cdc31p show defects i