Cells of Candida albicans WO-1 switch spontaneously and frequently between a white and an opaque CFU. Recently, an opaque-phase-specific cDNA, PEP1, was cloned and was demonstrated to code for a pepsinogen. By using a differential hybridization screen, a second opaque-phase-specific cDNA, Op4, has been isolated and its corresponding gene has been cloned. Op4 is coordinately regulated with PEP1 but resides on a different chromosome. During temperature-induced mass conversion from opaque to white, transcription of PEP1 and Op4 is immediately inhibited by the increase in temperature, but transcription of both genes can be rapidly reestablished by a downshift in temperature prior to phenotypic commitment. However, the capacity to rapidly induce both PEP1 and Op4 is lost coincidentally with the second semisynchronous round of cell division and phenotypic commitment during mass conversion. Op4 shows no significant base or amino acid sequence homology with a known gene or protein, respectively. However, the deduced Op4 protein exhibits several interesting characteristics, including a hydrophobic amino terminus with 26 amino acids, a pI of 10.73 for the last 100 amino acids, two serine repeats adjacent to alanine repeats, and the potential for alpha-helical conformation within the alanine-rich sequences. No genomic reorganization was evident in the proximity of Op4 during transcriptional activation and deactivation accompanying the white-opaque transition.
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