No abstract

Killer strains of Saccharomyces cerevisiae contain two species of doublestranded ribonucleic acid (dsRNA) with molecular weights estimated at 2.5 x 106 (L) and 1.4 x 106 (M). The M component appears to have a high adenine content. All mutants of killer which are defective for both the toxin and immunity functions lack the M dsRNA. One of these mutants has a novel dsRNA with a molecular weight of 5 x 105. Another class of killer mutants contains strains which are defective for either the toxin or the immunity function. They include temperature-sensitive killers, superkillers, and immunity-minus strains. The dsRNA profile of temperature-sensitive killers resembles that of the standard killer. The superkiller has 2.5 times more of the M dsRNA (1.4 x 106 daltons) than does the standard killer. Immunity-minus killers have, in addition to the two dsRNAs species of standard killer, a novel dsRNA with a molecular weight of 2.5 x 105. The data are consistent with the hypothesis that the M RNA controls toxin production. In addition, the two RNAs, L and M, seem to be regulated together. When the M RNA is missing, the amount of L is either greatly elevated or greatly reduced.

Purified and unstained nuclei were isolated from the leaves of several Gossypium species (diploid and tetraploid) by means of a citrate buffer (pH 5.0), Triton X-100 (5%), and a reducing sugar (1M glucose). DNA, previously unobtainable, was then extracted from the nuclei by conventional means. Comparisons of final DNA yield were made between three methods of purification: namely, the standardized ribonuclease procedure, hydroxyapatite chromatography and equilibrium density centrifugation in cesium chloride. The latter method produce the lowest, yet purest, yield of DNA for renaturation studies in Gossypium.

The DNAs of two diploid species of Gossypium, G. herbaceum var. africanum (A1 genome) and G. raimondii (D5 genome), and the allotetraploid species, G. hirsutum (Ah and Dh genomes), were characterized by kinetic analyses of single copy and repetitive sequences. Estimated haploid genome sizes of A1 and D5 were 1.04 pg and 0.68 pg, respectively, in approximate agreement with cytological observations that A genome chromosomes are about twice the size of D genome chromosomes. This differences in genome size was accounted for entirely by differences in the major repetitive fraction (0.56 pg versus 0.20 pg), as single copy fractions of the two genomes were essentially identical (0.41 pg for A1 and 0.43 pg for D5). Kinetic analyses and thermal denaturation measurements of single copy duplexes from reciprocal intergenomic hybridizations showed considerable sequence similarity between A1 and D5 genomes (77% duplex formation with an average thermal depression of 6 °C). Moreover, little sequence divergence was detectable between diploid single copy sequences and their corresponding genomes in the allotetraploid, consistent with previous chromosome pairing observations in interspecific F1 hybrids.

When the RNA from both the nucleus and polysomes of germinated cotton seeds were fractionated on poly(U)-cellulose columns it was found that both contained poly(A)-RNA. In ungerminated seeds most of the poly(A)-RNA is located in the nucleus of the cell. 3'-Deoxyadenosine was found to inhibit the synthesis of both nuclear and polysomal poly(A) by 75% in germinated seeds, but had little or no effect on protein synthesis during the first 6 hr of germination. After this time 3'-deoxyadenosine had a pronounced inhibitory effect on protein synthesis presumably due to the inhibition of poly(A) addition to newly synthesized mRNA.