Karl Pedersen

Maize Storage Proteins: Characterization and Biosynthesis

Developing seeds provide plant molecular biologists with useful model systems for studying the physiological and genetic mechanisms regulating the synthesis of specific plant proteins, i.e. seed storage proteins. These studies have perhaps even greater significance considering the importance of seed proteins in human and livestock nutrition. Maize storage proteins are interesting from both these aspects, since maize is an economically important crop and mutations affecting both the quantitative and qualitative synthesis of maize storage proteins have been identified (Mertz et al., 1964; Nelson et al., 1965). Our research in the last several years has been devoted to the characterization of these storage proteins and the reactions regulating their biosynthesis.

The zein proteins of maize endosperm

Abstract The storage protein in maize seed is composed of a group of alcohol-soluble polypeptides called zeins. These proteins are synthesized and deposited in the endosperm during seed development and are metabolized during seed germination.

Investigation of the complexity of barley stripe mosaic virus RNAs with recombinant dna clones

RNA isolated from the Type, ND18, and Norwich strains of barley stripe mosaic virus (BSMV) was electrophoresed in agarose gels, transferred to nitrocellulose, and hybridized with BSMV-specific complementary DNA (cDNA) or recombinant DNA clones derived from ND18 RNA. Genomic RNA components 1 (Mr = 1.43 x 10(6)) and 2 (Mr = 1.24 x 10(6)) were resolved in all three strains, but RNA 3 (Mr = 1.1 x 10(6)) was seen only in the ND18 and Norwich strains. A low-molecular-weight RNA (Mr = 0.27 x 10(6)), thought to be a subgenomic (SG) RNA, was also detected in RNA preparations from all three strains by staining with toluidine blue or ethidium bromide and by hybridizing with cDNA or selected recombinant DNA probes. Three classes of recombinant DNA clones, designated pBSM1, pBSM2, and pBSM3, were identified by hybridization of nick-translated recombinant DNA to electrophoretically separated viral RNAs. Clones in the pBSM1 class hybridized only to RNA 1 of all three strains and class pBSM2 clones hybridized only to RNA 2 of all three strains. Class pBSM3 clones hybridized to RNA 3 of the ND18 and Norwich strains and to RNA 2 of the Type strain, but not to RNA 2 of ND18 or Norwich. Based on the sizes of the BSMV-specified inserts in clones designated pBSM1a, pBSM2a, and pBSM3a, we estimate that a minimum of 44, 63, and 63% of the nucleotide sequences of ND18 and Norwich RNAs 1, 2, and 3, respectively, are unique. Furthermore, because the combined size of the inserts in pBSM2a and pBSM3a is approximately 15% greater than the estimated size of RNA 2, it is probable that the second RNA component of the Type strain actually consists of two RNA species which are similar in size but have different sequences. The SG RNA component is viral specific and contains sequences common to clones derived from RNA 3.

Stimulation of transcription by a soluble factor isolated from soybean hypocotyl by 2,4-D affinity chromatography

Abstract When crude extracts from soybean hypocotyl are passed through a column of 2,4-dichlorophenoxyacetic acid (2,4-D) substituted Sepharose, a small amount of protein is retained which can be eluted with 2 mM KOH. This KOH eluate contains a transcription factor that stimulates RNA synthesis 2–7-fold using E. coli RNA polymerase and native calf thymus DNA. Experiments using soybean multiple RNA polymerases separated by anion-exchange chromatography show that the factor stimulates the nucleolar enzyme (polymerase I), but not polymerases II and III. These results are discussed in relation to the involvement of auxin receptors in the enhancement of RNA polymerase I by auxin.

Structure and Expression of Zein Genes in Maize Endosperm

The storage proteins of maize seed are a group of alcohol-soluble proteins called zeins. These proteins can be separated by SDS polyacrylamide gel electrophoresis into four major groups that have apparent mol wts of 22,000, 19,000, 15,000 and 10,000 (Lee et al., 1976; Gianazza et al., 1977). The Mr 22,000 and Mr 19,000 components are made up of several polypeptides. Their NH2-terminal sequences are heterogeneous (Larkins et al., 1980) and on 2-dimensional polyacrylamide gels they show substantial charge heterogeneity (Hagen and Rubenstein, 1981). The Mr 15,000 and Mr 10,000 polypeptides are less heterogeneous, and appear to consist of only one or two proteins (Hurkman et al., 1981). Charge heterogeneity among different zeins is genotype specific (Righetti et al., 1977) and has been shown in several instances to be inherited in a simple Mendelian fashion (Soave et al., 1978). These studies suggest that the zeins are a highly homologous group of proteins encoded by multiple and closely related genes.