Figure 2.

SFH proteins can rescue growth and secretory defects associated with Sec14p dysfunction. (A) Schematic alignment of SFH gene products (also identified by their yeast genome database accession numbers) with Sec14p. Regions of homology are shaded, and the primary sequence identities/similarities shared by individual SFH gene products with Sec14p are given as percentages. (B) Expression of SFH2, SFH4, and SFH5 genes rescues the growth defects of sec14^ts and Δsec14 yeast mutants. Growth properties of a sec14-1^ts yeast strain (CTY1-1A) carrying YEp(SEC14) and YEp(URA3) as respective positive and negative controls for phenotypic complementation of the sec14-1^ts growth defect at 37°C are as indicated. Growth properties of strain CTY1-1A carrying YEp(SFH2), YEp(SFH3), YEp(SFH4), or YEp(SFH5) are also shown. All yeast strains were streaked for isolation onto YPD plates and incubated at either a permissive (25°C) or a restrictive (37°C) temperature for sec14-1^ts strains, as indicated. After 48 h of incubation, the growth results were recorded. YEp(SFH2) and YEp(SFH4) were nearly as effective as YEp(SEC14) in rescuing growth of the sec14-1^ts strain at 37°C. YEp(SFH5) was less effective, and YEp(SFH3) was ineffective. (C) Expression of SFH2, SFH3, SFH4, and SFH5 increases invertase secretion efficiency in sec14^ts strains at 37°C. Invertase secretion indices (i.e., measures of secretory function) were determined (see MATERIALS AND METHODS). Wild-type strains secrete invertase efficiently (secretion index ≥ 0.90), and Sec14p-insufficient cells secrete invertase poorly (secretion index ≤ 0.20). Each YEp(SFH) expression cassette markedly improved secretory pathway function under conditions of Sec14p deficiency. Values represent averages of at least three independent trials with triplicate determinations for each strain.