Figure 4. Cell volume profiles for the diploid histone deletion
strains. The size distributions of cells from early logarithmic growth
cultures were measured as described in Materials and Methods.
The histogram of the number of cells in each channel is plotted
against the cell volume of the channel. The results were separated
into two panels for clarity. The distribution for the wild-type strain
MSY167 is indicated by the open circles in both plots. The profile
for the copy-I deletion diploid MSY164 is illustrated in the open triangles
in a and the profile for the copy-II deletion diploid MSY165
is shown in the open squares in b.
increase in the average generation time and cell size for the
H3-H4 deletion mutants (41). We reasoned that the decreased
gene dosage of the H3 and H4 genes in the homozygous deletions
might lead to an increase in the length of the S-phase
of the cell cycle due to a defect in chromatin assembly. While
we will show below that this is not the case, it was clearly
of interest to obtain an estimate of the cell cycle timing in the
deletion strains.
The cell cycle periods of the strains were examined by flow
microfluorometry (44). For these experiments we used the
set of diploid strains from cultures grown in YPD medium.
We were unable to obtain reliable results from the haploid
cells because of the low fluorescence signal from cells with
G1 haploid DNA content. Diploid wild-type or histone gene
deletion cells from early log phase cultures were harvested