Variable aberrant cDNAs in single diphtheria toxin-resistant human fibroblasts.

We treated transformed human fibroblasts with diphtheria toxin (DT) and isolated 40 single cells that were toxin resistant but unable to propagate. In 13 of them toxin resistance was associated with the presence of one or more aberrant transcripts of the structural gene for elongation factor 2 (EF-2). cDNA obtained from these transcripts had 164-447 bp-long deletions. Each of these deletions was associated with 2-8 base pairs-long repeats at its breakpoints. Only 10 out of 16 cDNA deletions were associated with presumed exon junctions. A role is suggested for errors in transcription in producing the aberrant transcripts which gave rise to the deletion-bearing cDNA species.

The differences among Jewish communities--maternal and paternal contributions.

The haplotypes of Y chromosome (paternally inherited) and mtDNA (maternally inherited) were analyzed in representatives of six Jewish communities (Ashkenazic, North African, Near Eastern, Yemenite, Minor Asian/Balkanian, and Ethiopian). For both elements, the Ethiopian community has a mixture of typically African and typically Caucasian haplotypes and is significantly different from all others. The other communities, whose haplotypes are mostly Caucasian, are more closely related; significant differences that were found among some of them possibly indicate the effects of admixture with neighboring communities of non-Jews. The different contribution of the Y chromosome and mtDNA haplotypes to the significant differences among the communities can be explained by unequal involvement of males and females in the different admixtures. In all communities, except the Ethiopians, the level of diversity (h) for Y chromosome haplotypes is higher than that for mtDNA haplotypes, suggesting that in each community the people who become parents include more males than females. An opposite proportion (more females than males) is found among the Ethiopians.

Annealing of alkali-resistant HSV DNA strands and isolation of S and L components.

DNA isolated from highly purified virions of herpes simplex virus type-1 (HF strain) was denatured by centrifugation in alkaline sucrose gradients. DNA molecules corresponding to intact single-stranded virion DNA (50 x 10(6) daltons) were isolated and adjusted to neutral pH. The DNA was annealed under conditions permitting reassociation of intact single-stranded molecules and studied by electron microscopy. Three classes of DNA molecules showing double-stranded sequences were observed: (a) fully double-stranded DNA molecules the size of the intact HSV DNA genome, namely 52 micron; (b) DNA hybrids with a region of partial double-strandedness ranging from 5 to 12 micron, plus long single strands; and (c) DNA hybrids with a double-stranded region of 32--40 micron, plus short single strands. (These results suggest that the alkali-resistant single-stranded HSV DNA molecules are composed of several subclasses that permit annealing of either the total genome or the S or L components.) The 5 micron double-stranded region probably constitutes the S component of HSV DNA and the sequences longer than 5 micron and shorter than 12 micron represent annealing of the repeat sequences on either or both sides of the S component. The double-stranded sequences with a length of 32--40 micron may represent the L component. Treatment of the annealed, partially double-stranded hybrid DNA molecules with S1 endonuclease to remove the single-stranded termini and centrifugation in neutral sucrose gradients yielded two distinct peaks. Centrifugation of fractions from the two peaks in caesium chloride density gradients showed that the small DNA component (possibly the S and the repeat sequences) had a higher buoyant density and the longer (possibly the L) DNA component had a lower density than the HSV DNA marker. Annealing of alkali-resistant viral DNA strands therefore provides a means of isolating the L, S and repeat sequence regions of HSV DNA.