The binding of pentaammineruthenium (III) to RNase B and RNase A+d(pA)4 in the crystalline state

The binding of pentaammineruthenium (III) to ribonuclease A and B both free and complexed with d(pA)₄ has been examined in the crystalline state through the application of X-ray diffraction and difference Fourier techniques. In crystals of native RNase B, the reagent was observed to have many binding sites, some entirely electrostatic in nature and others consistent with coordination to histidine residues. The primary histidine in the latter case was 105 with 119 also partially substituted. In crystals of RNase A+d(pA)₄ complex only a single, extremely strong site of substitution was observed, and this was 2.4 Å from the native position of the imidazole ring of histidine 105. Thus, the results of these X-ray diffraction studies appear to be quite consistent with the findings of earlier NMR studies and with the results obtained in crystals of the gene 5 DNA binding protein.     

EFFECTS OF X IRRADIATION ON LEMNA PERPUSILLA

Posner , Herbert B., and William S. Hillman . (Yale U., New Haven, Conn.) Effects of x irradiation on Lemna perpusilla. Amer. Jour. Bot. 47(6): 506–511. Illus. 1960.—The effects of x rays on the multiplication rates (MR), percent flowering (Fl%) and gross morphology of aseptically grown cultures of Lemna perpusilla, strain 6746, were studied. MR values are unaffected by doses of less than 300 r but are progressively depressed as the dose increases. The effect of a given dose on short-term MR values is the same at the 2 dosage intensities used, 500 and 2000 r/min. The inhibitory effect of intermediate doses on long-term growth is delayed; high doses have an “immediate” effect. Bleaching of fronds and cessation of growth occur in all cultures given 5,000 r or higher. Radiosensitivity is not altered by addition of yeast extract and casein hydrolysate to the medium. Depressed Fl% and seed production appear to be consequences of lowered MR. Morphological aberrations such as small size, epinasty and wrinkling are temporary. Frond-sequence may be altered by x rays but this aberration is permanent. Various aspects of the results are discussed.