Previous studies have suggested that the R locus of maize is responsible for determining the temporal and spatial pattern ofanthocyanin pigmentation in the plant. In this report we demonstrate that three members of the R gene family, P, S, and Lc, encode homologous transcripts 2.5 kilobases in length. The structure of one R gene, Lc, was determined by sequencing cDNA and genomic clones. The putative Lc protein, deduced from the cDNA sequence, is composed of 610 amino acids and has homology to the helixloop-helix DNA-binding/dimerization motif found in the Lmyc gene product and other regulatory proteins. It also contains a large acidic domain that may be involved in transcriptional activation. Consistent with its proposed role as a transcriptional activator is our finding that a functional R gene is required for the accumulation of transcripts of at least two genes in the anthocyanin biosynthetic pathway. We discuss the possibility that the diverse patterns of anthocyanin pigmentation conditioned by different R genes reflect differences in the R gene promoters rather than their gene products.The anthocyanin biosynthetic pathway of maize has proven to be an ideal system for understanding genetic interactions between regulatory and structural genes (for review see ref.

The wx-K mutation results from the insertion of a copia-like retrotransposon into exon 12 of the maize waxy gene.

The Drosophila melanogaster ribosomal DNA (rDNA) functions as an X-Y meiotic pairing site. Deletions encompassing the X chromosomal rDNA block (located in the heterochromatin) disrupt X-Y pairing and disjunction. Insertions of single, complete rRNA genes at ectopic locations on the heterochromatically deficient X partially restore X-Y pairing capacity. This study was undertaken to test fragments of an rDNA repeat for the ability to stimulate X-Y pairing and disjunction and to test for relationships between pairing capacity and two other phenotypes associated with rDNA insertions: transcription and the ability to organize a nucleolus. Insertions of three different fragments, all of which retained the rDNA promoter and upstream spacer sequences and which differed among each other in the length of downstream sequences, were obtained by P-element mediated transformation. One of the fragments is truncated only 140bp downstream from the promoter. Insertions of all three fragments proved capable of stimulating X-Y disjunction. Double insertions were substantially more effective than single insertions. RNA/PCR analysis was used to show that transcripts initiated at the inserted rDNA promoters are present in testis RNA from all insertions. Treatment with an antinucleolar antibody revealed that none of the insertions was associated with a mininucleolus. Thus promoter-containing rDNA fragments are autonomously capable of being transcribed and of functioning as X-Y pairing sites, but not of forming a mini-nucleolus.

The complete sequence of a Tennessee isolate of maize chlorotic dwarf virus (MCDV-TN) was determined from cDNA clones and by direct sequencing of the viral RNA. The genome is 11 813 nucleotides (nt) in length and contains one large open reading frame between nt 435 and 10763 that encodes a polyprotein of 3443 amino acids. The Nterminal amino acid sequences were determined for the three capsid proteins. All three were adjacent,

In Drosophila melanogaster males, X-Y meiotic chromosome pairing is mediated by the nucleolus organizers (NOs) which are located in the X heterochromatin (Xh) and near the Y centromere. Deficiencies for Xh disrupt X-Y meiotic pairing and cause high frequencies of X-Y nondisjunction. Insertion of cloned rRNA genes on an Xh- chromosome partially restores normal X-Y pairing and disjunction. To map the sequences within an inserted, X-linked rRNA gene responsible for stimulating X-Y pairing, partial deletions were generated by P element-mediated destabilization of the insert. Complete deletions of the rRNA transcription unit did not interfere with the ability to stimulate X-Y pairing as long as most of the intergenic spacer (IGS) remained. Within groups of deletions that lacked the entire transcription unit and differed only in length of residual IGS material, pairing ability was proportional to the dose of 240-bp intergenic spacer repeats. Deletions of the complete rRNA transcription unit or the 28S sequences alone blocked nucleolus formation, as determined by binding of an antinucleolar antibody, yet did not interfere with pairing ability, suggesting that X-Y pairing may not be mechanistically related to nucleolus formation. A model for achiasmatic pairing in Drosophila males based upon the combined action of topoisomerase I and a strand transferase is proposed.

No abstract

The 3'-terminal 1902 nucleotides of the tobacco vein-banding mosaic virus (TVBMV) were cloned and sequenced. The sequence contains a large open reading frame of 572 amino acid residues followed by a non-coding region of 183 nucleotides which terminates in a polyadenylate tract. The TVBMV coat protein is processed from a larger polyprotein by cleavage at a Gln/Gly dipeptide, which is followed closely by the aphid transmission DAG triplet. Translation of the nucleotide sequence yielded a protein of 271 amino acid residues with a calculated M(r) of 30,347. The amino acid and nucleotide sequences of the TVBMV coat protein and 3' non-coding region were compared to 33-35 other virus sequences. Percent sequence identity of the amino acid and nucleotide sequences were in the range expected from comparison of distinct viruses. Phylogenetic analyses were also performed to determine the relationship of TVBMV to other well-characterized viruses. These studies indicate that TVBMV should be regarded as a distinct member of the potyvirus group.

In 1993, stunted field-grown daikon radish plants were found with black lesions on the petioles and leaf blades, and new growth exhibited leaf crinkling and a mosaic pattern on distorted leaves. The plants had hollow roots and seed production was severely reduced. Symptomatic plants contained isometric virions identified as those of turnip crinkle virus (TCV). This is the first report of TCV causing serious economic damage and the first report of natural infection in North America. ZusammenfassungNaturUcher Befall im Freiland wachsender Daikon-Rettiche (Raphanus sativus L.) durch das Tninip crinkle virus in Nordamerika 1993 wurden im Freiland kummemde Exemplare des Daikon-Rettichs gefunden, die schwarze Lasionen auf Blattstielen und Blattspreiten trugen. Die jungen Blatter waren deformiert und gekrauselt, zudem wiesen sie ein Mosaik auf. Die Pflanzen batten hohle Wurzeln und biideten nur wenige Samen. Pflanzen mit diesen Symptomen enthielten isometrische Virionen, die als diejenigen des Turnip crinkle virus (TCV) identifiziert wurden. Dies ist der erste Bericht tlber starke TCV-bedingte Schaden und uber einen nattirlichen Befall in Nordamerika.