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SUMMARY The wall mannan in dividing Saccharomyces cells was labelled by exposing the yeasts to fluorescein-conjugated concanavalin A. The yeasts were then allowed to grow in the absence of excess staining reagent and were examined by fluorescence microscopy at several intervals after the re-initiation of growth. The newly synthesized mannan was non-fluorescent and, thus, could be easily distinguished from the material present at the outset. Most new mannan was deposited in the wall surrounding the bud, and little if any of the mannan in the bud wall was derived from the surface of the mother cell. Deposition of new mannan in the mother cell was detected only in the bud scar. The distal tip of the growing bud was identified as the major site at which new mannan was inserted into the existing wall fabric. This area is also known to be the deposition site of newly synthesized glucan. Thus, with respect to these two major wall polysaccharides, wall replication in Saccharomyces cells resembles the apical mode exhibited by filamentous fungi.
Tkacz et al. (Fri,) studied this question.