Flocculation of Saccharomyces cerevisiae is induced by transformation withthe GAP1 gene from Kluyveromyces marxianus

A non-flocculent strain of Saccharomyces cerevisiae was transformed with th e GAP1 gene which encodes p37, a GAPDH-like protein present in the cell wal l of Kluyveromyces marxianus flocculent cells. The transformed cells were c haracterized with respect to flocculation behaviour, morphology, growth, ce ll wall integrity and GAPDH activity. A flocculent phenotype was acquired b y the transformed cells, showing a behaviour in respect to flocculation/def locculation very similar to that of K. marxianus. The presence of p37 in th e cell wall was assessed by immunoprecipitation of biotinylated cell wall p roteins and an accumulation of p37 was evident in the cell wall of transfor med cells. This result was confirmed by studies using a chimeric protein re sulting from fusing the p37 with a yeast-enhanced green fluorescent protein , yEGFP. The recombinant protein was localized mainly in the cell wall of t he transformed strain, although the presence of p37 in the cytosol was indi cated by an increase in GAPDH activity. Calcofluor white sensitivity tests indicated that the cell wall structure is affected by the accumulation of p 37. These results provided further evidence of p37 function regarding flocc ulation and that although lacking a N-terminal signal peptide p37 is target ed to the cell wall. Copyright (C) 2000 John Wiley & Sons, Ltd.