Stable and unstable mutations in aberrant ratio stocks of maize.

Aberrant Ratio (AR) stocks of maize were tested for transposition activity. Lines exhibiting AR and homozygous for the dominant alleles at the Sh Bz and Wx loci in the short arm of chromosome 9 were crossed as males to a sh bz wx tester. Among a population of 346,201 kernels, eight mutations of sh and two of bz were recovered. Eight of the ten mutations survived and none was as vigorous as its normal sibs. At least five of the sh mutants appear to be unstable in F(2 ) and subsequent generations. An unexpected observation was the high incidence of somatic loss of chromosome 9 markers (Sh Bz and Wx), indicating chromosome breakage or nondisjunction. Southern blot hybridization analysis of the sh alterations indicate that all but one mutant are associated with structural DNA rearrangements at the shrunken locus. Possible mechanisms by which these alterations arose are discussed.

Structural forms and transitions for the complex of mercury(II) with poly(dG-dC).

Infrared spectroscopy was used to study hydrated double-helical poly(dG-dC) complexed with varying amounts of mercury(II). For one Hg(II) per ten nucleotide residues (r = 0.1), the B structure was stabilized and the B* structure was absent at high hydration. The Z structure did not form as hydration was reduced. For r = 0.2, the B and Z structures coexisted at high hydration and the transition to total Z structure was broad as hydration was reduced. Hg(II) was bound exclusively to the guanine residues probably at N3 or N7 for r less than or equal to 0.25. The cytosine residue did not protonate (at N3) as Hg(II) was bound to guanine. The addition of NaCl together with Hg(II) reduced the binding of Hg(II), stabilized the B structure at the highest hydration and caused a sharp transition between the B and Z structures as hydration was lowered. Hydration with D2O stabilized the Z structure for poly(dG-dC) complexed with HgCl2.

Structural forms and transitions of poly(dG-dC) with Cd(II), Ag(I) and NaNO3.

Infrared spectroscopy was used to study the structures and transitions in hydrated gels of double-helical poly(dG-dC) complexed with the metal carcinogens Cd(II) and Ag(I). For one Cd(II) per ten nucleotides (r = 0.1), the B structure was stable at high and moderate hydrations with D2O and the B and Z structures coexisted at low hydrations. For poly(dG-dC) with Cd(II) at r = 0.2 to 0.35, the Z structure was stable at high hydrations (94% r.h. for r = 0.2). At a given value of hydration, H2O gave a higher content of Z structure than D2O. Cd(II) most likely binds to guanine residues at N7 in both the B and Z forms of poly(dG-dC) but binding to guanine N3 can not be excluded. It is unlikely that Cd(II) binds to cytosine residues at the r values studied and the cytosine residues did not protonate at N3 as Cd(II) bound to guanine residues. Poly(dG-dC) with Ag(I) at r = 0.2 to 0.36, existed in a B-family structure which is different from the B-family structure of the type I complex of Ag(I) and calf-thymus DNA. Poly(dG-dC) with Ag(I) did not assume the Z structure at lower hydrations even though NO3- was present in the sample. Ag(I) differs from other soft-metal acids which promote the Z structure. Ag(I) most likely binds to the guanine N7 or N3 and not to cytosine residues. Cytosine residues did not protonate at N3 as Ag(I) was bound to guanine.(ABSTRACT TRUNCATED AT 250 WORDS)

Structural forms, stabilities and transitions in double-helical poly(dG-dC) as a function of hydration and NaCl content. An infrared spectroscopic study.

The poly(dG-dC) helical duplex forms a modified, B-family structure (B*) at very high hydration and a normal B structure at slightly lower hydration. The B* structure is slightly different in sugar-phosphate and base-stacking conformations than the B structure. Increasing the hydration or decreasing the NaCl content stabilizes B* with respect to B. Poly(dG-dC) forms the Z structure at low NaCl contents when the hydration is sufficiently reduced. At moderate NaCl content, the B to Z transition is sharp and cooperative for hydration with D2O. Hydration with H2O broadens the transition which occurs at lower hydration. This suggests that hydrogen bonding is stronger in the Z structure and helps stabilize Z over B. IR spectra may be used to quantitatively estimate the fractions of B and Z structures present in a sample. Some new indicator bands are described.

The infrared spectrum and structure of the type I complex of silver and DNA.

Infrared spectroscopy was used to study films of the type I complex of Ag+ and DNA as a function of hydration with the following conclusions. Ag+ binds to guanine residues but not to cytosine or thymine residues. Cytosine becomes protonated as Ag+ binds to guanine. (These conclusions confirm previous models.) The type I complex remains in the B family of structures with slight modifications of the sugar-phosphate geometry. This modified B structure remains stable at lower values of hydration for which pure DNA is in the A form. Binding of Ag+ to PO2-, O-P-O or the deoxyribose oxygen is excluded.

Isolation of eukaryotic initiation factor 2 from yeast Saccharomyces cerevisiae.

Protein synthesis initiation factor eIF-2 has been isolated from the high speed supernatant fraction of the yeast Saccharomyces cerevisiae. This purification steps include ammonium sulfate fractionation, column chromatography on Sephacryl 300 and hydroxyapatite, and glycerol gradient sedimentation. Electrophoresis of the purified factor on sodium dodecyl sulfate polyacrylamide gels reveals three polypeptides with a total Mr of 127,000. The molecular weights of the subunits are 31,000, 46,500, and 49,600. The pI of each of these subunits is 4.5, 7.3, and 8.6, respectively. The stoichiometry of the subunits varies from 1:1:1 to 1:0.25:1 suggesting that the active factor may be composed of only two subunits with total Mr of 80,000. The factor is part of a high molecular weight complex during the first steps of the purification. Prior to chromatography on Sephacryl, this complex is broken up in high salt. The activity of the factor is stabilized by inclusion of GDP in all buffers during the preparation and is stimulated by magnesium ion.