ALTERED MAIZE ENDOSPERM ADP-GLUCOSE PYROPHOSPHORYLASES FROM REVERTANTS OF A <i>SHRUNKEN-2-DISSOCIATION ALLELE</i>

ABSTRACT Four phenotypically wild-type seeds were obtained from separate Activator-induced events in the Dissociation-inhibited allele sh2-ml (shrunken-2, mutable-1). Endosperm adenosine diphosphoglucose pyrophosphorylase, the enzyme controlled by sh2, was extracted and partially purified from the four revertants and was compared to enzyme produced by the progenitor Sh2 allele and the sh2-m allele. The revertants contained 50 to 140% of the activity conditioned by the progenitor allele. Each of the revertants appears to be unique as judged by differences in Km(glucose-1-PO4), 3-phosphoglycerate(3-PGA) activation, and phosphate-inhibition. In one case the reversion event apparently increased the sensitivity of ADP-glucose pyrophosphorylate to 3-PGA activation.</jats:p

Poliovirus RNA-dependent RNA polymerase and host cell protein synthesize product RNA twice the size of poliovirion RNA in vitro

The poliovirus RNA-dependent RNA polymerase required an oligouridylate primer or a HeLa cell protein (host factor) to initiate RNA synthesis on poliovirion RNA in vitro. The polymerase synthesized template-sized product RNA in the oligouridylate-primed reaction. In the host factor-dependent reaction, the largest product RNA synthesized by the polymerase was twice the size of the template RNA. About half of the product RNA recovered from this reaction was shown to exist in the form of a snapback sequence. Time-course reactions and pulse-chase experiments showed that the product RNA was only slightly larger than the template RNA at early reaction times and that with time it increased in size to form the dimer-sized product RNA. Inhibition of the elongation reaction by adding only [alpha-32P]UTP and ATP resulted in the formation of template-sized product RNA. The dimer-sized product RNA was unaffected by phenol extraction or proteinase K treatment but was converted to template-sized molecules by S1 nuclease. Dimer-sized poliovirus RNA that was sensitive to S1 nuclease was also isolated from poliovirus-infected cells. The results from this study indicate that the labeled negative-strand product RNA synthesized in vitro was covalently linked to the positive-strand template RNA. Thus, in vitro, the primer-dependent poliovirus RNA polymerase may initiate RNA synthesis in the presence of the host factor by using the 3' end of the template RNA as a primer.</jats:p

MULTIPLE FORMS OF MAIZE ENDOSPERM ADP-GLUCOSE PYROPHOSPHORYLASE AND THEIR CONTROL BY SHRUNKEN-2 AND BRITTLE-2

ABSTRACT Heat-labile and heat stable forms of ADP-glucose pyrophosphorylase were identified in the maize endosperm. The heat-labile form is destroyed by normal electrophoretic conditions. The heat-stable form corresponds to pyrophosphorylase B. In wild type, 96% of the total activity is heat labile. Both forms are reduced in 11 brittle-2 (bt2) and 12 shrunken-2 (sh2) mutants. The heat-labile form is reduced to a greater extent than is the heat-stable form in each of the 23 mutants. Deletion of sh2 abolishes both forms. The original ratio of the two forms is restored after sh2 function is expressed via transposition of Dissociation from sh2. The possible roles of these genes in the control of ADP-glucose pyrophosphorylase are discussed.</jats:p