DISTRIBUTION OF THE FLOCCULATION PROTEIN, FLOP, AT THE CELL-SURFACE DURING YEAST GROWTH - THE AVAILABILITY OF FLOP DETERMINES THE FLOCCULATION LEVEL

The yeast FLO genes encode cell surface proteins which are expected to play a major role in the control of flocculation. We have assessed th e availability of the Flo proteins at the cell surface during the grow th of two flocculent strains, ABXL-1D (FLO1) and STX347-1D (FLO5) usin g immunological approaches, enzyme-linked immunosorbent assays and imm unofluorescence. Our data show that they are not permanently present a t the cell surface but that their amount increases during growth. With both strains the flocculation level is tightly correlated to the amou nt of Flop antigen detected, suggesting that it is the availability of the Flo proteins at the cell surface which determines the flocculatio n level. Our data are consistent with the idea that the Flo proteins c orrespond to the flocculation lectins. The differences of flocculation pattern among strains could originate from variations in the regulati on of the expression of the FLO genes. Monitoring of the distribution of the Flo proteins during cellular development revealed that they are incorporated essentially in the cell wall of growing buds. Incorporat ion of the Flo proteins in the cell wall displays a highly polarized a spect, at the bud tip and at the mother-daughter neck junction, which can persist in mature cells. Such a localization could be relevant to constraints of the cell wall incorporation of the mannoproteins. Depen ding on the regulation of Flop expression and on the incorporation of the proteins in the cell wall, a yeast population can be highly hetero geneous in Flo protein equipment. (C) 1998 John Wiley & Sons, Ltd.