Caulobacter flagellin mRNA segregates asymmetrically at cell division

Abstract

Molecular processes which promote the spatial localization of subcellular components are fundamental to cell development and differentiation. At various stages in development unequal segregation of molecular information must occur to result in the differentiated characteristics which distinguish cell progeny. Biological attributes of the dimorphic bacterium, Caulobacter crescentus, provide an experimental system permitting examination of the generation of asymmetry at the molecular level¹. When a Caulobacter cell divides, two different daughter cells are produced—a motile swarmer cell with a polar flagellum and a non-motile cell with a static appendage referred to as a stalk. The two cell types are distinct with respect to surface morphology^2–5, developmental potential^1,6, protein composition⁷ and biosynthetic capabilities^8,9. One of the more conspicuous manifestations of asymmetric expression of macromolecules in this system, the flagellum, has been studied extensively^3,10–13. We have cloned the flagellin genes of Caulobacter¹⁴ and report here the use of these sequences as probes to demonstrate that (1) the level of flagellin mRNA is regulated during the cell cycle in a pattern coincident with flagellum polypeptide synthesis and (2) flagellin mRNA synthesized before cell division is segregated with progeny swarmer cells. This provides molecular evidence of specific partitioning of an mRNA at the time of cell division.