Ribosomal RNA processing in Candida albicans

Abstract

Ribosome assembly begins with conversion of a polycistronic precursor into 18S, 5.8S, and 25S rRNAs. In the ascomycete fungus Candida albicans, rRNA transcription starts 604 nt upstream of the 18S rRNA junction (site A1). One major internal processing site in the 59 external transcribed spacer (A0) occurs 108 nt from site A1. The A0-A1 fragment persists as a stable species during log phase growth and can be used to assess proliferation rates. Separation of the small and large subunit prerRNAs occurs at sites A2 and A3 in internal transcribed spacer-1 Saccharomyces cerevisiae pre-rRNA. However, the 59 end of the 5.8S rRNA is represented by only a 5.8S (S) form, and a 7S rRNA precursor of the 5.8S rRNA extends into internal transcribed spacer 1 to site A2, which differs from S. cerevisiae. External transcribed spacer 1 and internal transcribed spacers 1 and 2 show remarkable structural similarity with S. cerevisiae despite low sequence identity. Maturation of C. albicans rRNA resembles other eukaryotes in that processing can occur cotranscriptionally or post-transcriptionally. During rapid proliferation, U3 snoRNA-dependent processing occurs before large and small subunit rRNA separation, consistent with cotranscriptional processing. As cells pass the diauxic transition, the 18S pre-rRNA accumulates into stationary phase as a 23S species, possessing an intact 59 external transcribed spacer extending to site A3. Nutrient addition to starved cells results in the disappearance of the 23S rRNA, indicating a potential role in normal physiology. Therefore, C. albicans reveals new mechanisms that regulate post-versus cotranscriptional rRNA processing.

A Single Acetylation of 18 S rRNA Is Essential for Biogenesis of the Small Ribosomal Subunit in Saccharomyces cerevisiae

“…3A). As observed in the WT strain, 23 S pre-rRNA accumulated at high levels during stationary phase in both S. cerevisiae (34) and Candida albicans (35). Hence, 23 S pre-rRNA is a physiological precursor for 18 S rRNA formation in the WT strain.…”

Pseudouridine synthase 7 impacts Candida albicans rRNA processing and morphological plasticity

“…The presence of increased unprocessed rRNA and rRNA processing intermediates in pus7/pus7 , including 35S rRNA, was confirmed via northern blot probing for ITS2 (Figure c). Our results are consistent with previously described C. albicans rRNA processing intermediates (Pendrak & Roberts, ). Moreover, a number of cell surface protein transcripts were differentially regulated in pus7/pus7 , and we tested if this led to a change in cell surface hydrophobicity and biofilm formation.…”

Disruption of ribosome assembly in yeast blocks cotranscriptional pre-rRNA processing and affects the global hierarchy of ribosome biogenesis

“…Furthermore, when yeast cells are grown to high density, the frequency of cotranscriptional A 0 , A 1 , and A 2 cleavage decreases dramatically, suggesting that cotranscriptional pre-rRNA processing is regulated by cell growth and division (Osheim et al 2004). Consistent with these observations, it was recently shown that pre-rRNA in C. albicans is processed cotranscriptionally in rapidly dividing cells, but processed post-transcriptionally after cells undergo the diauxic shift (Pendrak and Roberts 2011).…”