The organization of the H3-H4 gene sets and their deletion derivatives is
summarized in Fig. 1. The copy-I deletion was constructed by Bal 31
nuclease digestion at the unique Sma I site in the intergene region between
the H3 and H4 genes. A set of Bal 31 digestion fragments was selected by
screening for fragment size on agarose gels and the DNA sequences of the
breakpoints were determined from M13 phage subclones of the fragments.
The leftward deletion breakpoint ends 186 bp downstream of the end of the
H3 transcript and 21 bp before the end of the open reading frame of the
SMTI gene. The rightward deletion breakpoint ends 185 bp past the end of
the H4-transcribed sequences and 73 bp past the histone ARS core consensus
sequence (3, 4). These left and right deletion fragments were joined
by an ECO RI synthetic DNA linker in the recombinant.
The copy-II deletion was constructed from restriction fragments flanking
the H3 and H4 genes. The lefthand section was a Hind III-Acc I fragment
from the yeast historic H3 clone Sc201 while the righthand section was the
Hind III-Eco RI fragment Sc218 that is adjacent to the H4-distal righthand
end of the yeast histone H4 clone Sc202 (Fig. 1). These two restriction fragments
were joined by a synthetic Bam HI linker.