Polyadenylation of ribosomal RNA by Candida albicans also involves the small subunit

We now present data that this process also involves the small 18S subunit of ribosomal RNA in this organism. Unlike the large 25S subunit, polyadenylation sites near the 3' end are more variable and no polyadenylation was found at the reported maturation site of 18S. Similar to 25S, one or more polyadenylated mature sized 18S molecules get intensified transiently by serum just prior to the appearance of hypha.The transient increase in polyadenylation of both the large and the small subunits of ribosomal RNA just prior to the appearance of hypha, raises the possibility of a role in this process.Candida species are now among the most important pathogens especially for the immunocompromised host. They are the fourth most common organisms recovered from blood cultures in hospitalized patients [1]. Candida albicans the most frequently isolated of the species, is a polymorphic organism. It can switch from a yeast form (blastospore) to a filamentous phase (hypha and pseudohypha) in response to a variety of external stimuli, including mammalian serum. Mutants defective in this serum response, also show a reduced capacity to cause disease in a murine model, [2] suggesting a virulence role for it.It is widely accepted that the production of the RNA components of ribosomes in eukaryotes proceeds through the transcription of large pre-RNA molecules by RNA polymerase I (Pol I), that get processed into the final large and small subsegments [3]. We have recently reported the unexpected finding that Candida albicans polyadenylates some of its 25S ribosomal RNA (rRNA) and the polyadenylation site corresponded to the large subsegment 3'-end maturation [4]. We also found that the concentration of the polyadenylated form of 25S was increased transiently by serum just prior to the appearance of filamentous forms, raising the possibility for a role in hyphal transformation. A question raised by these data was whether this event is unique for the large subunit rRNA or it represents a wide