Candida albicans generally grows in hyphal form in RPMI-1640 medium. However, transformation of hyphal form to yeast form is inhibited by declining pH in RPMI-1640 medium and low pH enhance the yeast like forming. The expressions of RAS1, EFG1, ALS1 and CYR1 mRNA in low pH conditions are significantly decreased compared with that of neutral pH conditions. These results suggested that the transformation of C. albicans may be regulated by pH-dependent stimulation system, and the system was regulated by RAS1 expression
