Absence of See1p, a widely conserved Saccharomyces cerevisiae protein, confers both deficient heterologous protein production and endocytosis.

The uncharacterized Saccharomyces cerevisiae open reading frame (ORF) YIL064w is predicted to encode a cytoplasmic 28 kDa protein, recognized by sequence similarity as a putative S-adenosyl-L-methionine methyltransferase. A micro-scale screening performed in our laboratory with the EUROSCARF S. cerevisiae BY4741 deletion mutant collection identified YIL064w deletion as negatively affecting secretory production of reporter alpha-amylase. The work presented here corroborates the later observations of the yil064w mutant in a larger-scale assay and shows that Yil064p is necessary for the efficient secretory production of two reporter proteins, murine alpha-amylase and fungal polygalacturonase. Further, we analysed endocytosis in the yil064w mutant strain and observed defects at both very early and later stages of endocytic transport in cells in the late logarithmic phase. The defects at very early stages may decisively account for the low transfection (DNA uptake by endocytosis) efficiency that we also observed in the yil064w mutant. These are the first in vivo data reporting a functional role for the protein encoded by ORF YIL064w and identify Yil064p, named here secretion and early endocytosis 1 protein (See1p), as a novel component of intracellular transport.