MOLECULAR-CLONING AND ANALYSIS OF THE YEAST FLOCCULATION GENE FLO1

The DNA sequence of the flocculation gene FLO1 of Saccharomyces cerevi siae, which is located on chromosome I (Watari et al., 1989) was deter mined. The sequence contains a large open reading frame (ORF) of 2586 bp and codes for a protein of 862 amino acids. However, further study (genomic Southern and polymerase chain reaction analyses) indicated th at the gene we cloned was not the intact FLO1 gene but a form with an approximately 2 kb deletion in the ORF region. The intact FLO1 gene wa s then cloned and its nucleotide sequence determined. The sequence rev ealed that the ORF of the intact gene is composed of 4611 bp which cod e for a protein of 1537 amino acids. A remarkable feature of the putat ive Flo1 protein is that it contains four families of repeated sequenc es composed of 18, 2, 3 and 3 repeats and that it has a large number o f serines and threonines. In the deleted FLO1 form, a large part of th ese repeated sequences was missing. The N- and C-terminal regions are hydrophobic and both contain a potential membrane-spanning region, sug gesting that the Flo1 protein is an integral membrane protein and a ce ll wall component.