Tetrads from diploid strains in which the deletion shuttle
plasmid had excised from one chromosome were dissected.
These dissections gave tetrads with four viable spores producing
two white and two red spore colonies. The red colonies
identified haploids in which the plasmid, and thus the
SUPllgene, had recombined out of the chromosome. This
excision results in one of two outcomes: either the wild-type
sequences are retained at the locus, or the deletion construction
replaces the wild-type genes. Genomic DNA preparations
from several red colonies were screened for the histone
gene deletions by Southern blot analysis. In this way deletions
of each of the H3-H4 loci were identified and confirmed
by restriction endonuclease mapping.