Control of morphogenesis in Candida albicans

• Main Author: Leng, P.
• Published: University of Aberdeen 1999
• Subjects: 572.8
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.592939

This thesis describes the cloning the characterisation of three <I>C. albicans</I> genes: <I>CaTBP1</I> encoding the TATA-binding protein, <I>CaRAD6</I> encoding a ubiquitin-conjugating (E2) enzyme, the <I>CaALS7</I> encoding an agglutinin-like cell-surface protein. Finally, the <I>ALS7</I> promoter has been discussed. The <I>CaTBP1</I> open reading frame is 716 bp long and encodes a functional TATA Binding Protein (TBP) of 27 kDa. Comparison of the predicted amino acid sequences of TBPs from a range of organisms reveals at least 80% amino acid sequence identity in the C-terminal domain. CaTbp1p binds specifically to a TATA box <I>in vitro</I>, substitutes for the human TBP to activate basal transcription <I>in vitro</I>, and suppress the lethal <I>Δspt15</I> (<I>tbp1</I>) mutation in <I>S. cerevisiae</I>. <I>CaRAD6</I> contains a 573-nucleotide ORF with the potential to encode a 179 amino acid polypeptide with a molecular mass of 19.7 kDa. The <I>CaRAD6</I> open reading frame is interrupted by two introns which both contain consensus splicing signal sequences. A comparison of the predicted amino acid sequences of Rad6 proteins from a range of organisms reveals strong conservation within their N-terminal domains (70% amino acid sequence identity). The <I>CaRAD6</I> gene complements the UV sensitivity and defective UV mutagenesis of a <I>S. cerevisiae</I> <I>rad6Δ </I>mutant. <I>RAD6</I> expression decreases during hyphal development in <I>C. albicans</I>. Elevated <I>RAD6</I> expression levels inhibit hyphal development, and Rad6p depletion enhances hyphal growth. These effects are dependent on the Efg1p morphogenetic signalling pathway. Therefore, <I>RAD6</I> is a negative regulator of hyphal development, revealing for the first time, a mechanistic link between ubiquitination and fungal morphogenesis. <I>CaALS7</I> is a member of the <I>ALS</I> gene family encoding agglutinin-like cell surface proteins in <I>C. albicans</I>. The <I>ALS7</I>sequence has a 3141-nucleotide open reading frame with the potential to encode a 1047 amino acid polypeptide.