Growth of Deletion Haploids
We next investigated the growth and cell cycle properties of
the viable histone deletion strains. Although the duplicated
H3-H4 loci were functionally redundant for cell viability, the
deletions need not have been phenotypically neutral. We first
looked at the behavior of the haploid deletion cells.
Strains deleted for either the copy-I or copy-II genes had
normal morphology and were neither temperature nor cold
sensitive for growth. The wild-type, copy-I deletion, and
copy-II deletion haploids were grown in YPD and synthetic
complete minimal liquid culture, and their growth rates were
measured. The doubling times for the strains are shown in
Table III. The growth rates in YPD medium were identical
for all three strains. Generation times were also very similar
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on the left of each panel illustrate the expected restriction fragments for the relevant genotypes and enzyme digestions. (A) The Southern
blots were probed with the copy-I Hind III fragment Sc191 (see Fig. 1). Since Sc191 includes the coding DNA of the H3 and H4 genes,
it will hybridize with the copy-II H3 and H4 coding sequences as well as the entire copy-I Sc191 region. Thus, the bands in the autoradiographs
are derived from either the wild-type copy-I locus, the copy-I deletion locus, or the wild-type copy-II locus. (B) The Southern
blots were probed with the copy-II-specific fragment Sc218 (Fig. 1). This fragment does not hybridize with sequences at the copy-I locus.
Therefore, the bands in the autoradiographs were derived from either the copy-II wild-type locus or the copy-II deletion locus.
in synthetic medium and the deletion haploids grew no more
than 5 % slower than wild-type cells. Both a- and a-haploid
strains for either copy-I or copy-II gene deletions were capable
of mating normally with haploids of the opposite mating
type. In short, no significant macroscopic phenotype was detected
for the deletion of either histone H3-H4 gene set.