The cytoplasmic localization of messenger RNA creates an asymmetric di
stribution of proteins that specify cell fate during development in mu
lticellular eukaryotes(1,2). The protein Ash1 is a cell-fate determina
nt in budding yeast which localizes preferentially to the presumptive
daughter nucleus, where it inhibits mating-type switching(3'4). Here w
e show that Ash1 mRNA is localized to the distal tip of daughter buds
in post-anaphase cells. Three-dimensional imaging reveals that Ash1 mR
NA is assembled into particles that associate with the cell cortex, To
achieve this localization, Ash1 mRNA must have its 3' untranslated re
gion and the actin cytoskeleton must be intact, Ash1 mRNA is not local
ized correctly in the absence of a myosin (Myo4) and is mislocalized t
o the mother-bud neck in the absence of a regulator of the actin cytos
keleton known as Bni1. We propose that Ash1 mRNA particles are transpo
rted into the daughter bud along actin filaments and are anchored at t
he distal tip. Thus, as in higher eukaryotes, Saccharomyces cerevisiae
employs RNA localization to generate an asymmetric distribution of pr
oteins and hence to determine cell fate.