TABLE 3

Allele specificity of the hpc2 interaction with spt16 mutations

Decrease in
MPT with HU
Growth at 30°
with HU
Effect with hpc2
Allelespt16-x plasmidspt16-x integrated
SPT16None+++ViableNone
spt16-G132D+++ViableWeak defect
spt16-4+++ViableND
spt16-6ND+++Strong defectND
spt16-7+++ViableND
spt16-8≥5°+Strong defectStrong defect
spt16-9ND-LethalND
spt16-11≥6°+DefectLethal
spt16-12+++Weak defectND
spt16-16ND+/-LethalND
spt16-22 (A417V)≥5°+/-LethalStrong defect
spt16-24≥4°+Weak defectND
  • Isogenic strains (7782-x) with the spt16 alleles indicated were placed on rich medium with or without 100 mm HU and the difference in maximal permissive temperature was determined as described in materials and methods. The effect of HU was not determined for alleles that we were unable to integrate, but the qualitative effect of HU on growth at 30° was assessed using strain 7737-3-2 carrying pTF128 (YCp LEU2 SPT16) with the allele of SPT16 indicated. Strain 8000-1-3 (spt16hpc2YCp-SPT16-URA3) was transformed with the same pTF128 derivatives and tested for growth on media containing 5-FOA at 26° to assess the effect of losing the SPT16 plasmid (“spt16-x plasmid”). The strength of the defect was scored on the basis of the growth rates observed at 26° and 30°. Selected alleles were also tested by reconstruction of the double mutant in standard genetic crosses (“spt16-x integrated”). The maximal permissive temperature of viable combinations was determined; “strong defect” indicates a drop of 5° or more, and “weak defect” indicates a drop of 1°-2°. ND, not determined.