Viral envelope fusion proteins are important structural proteins that mediate viral entry and may affect or determine the host range of a virus. The acquisition, exchange, and evolution of such envelope proteins may dramatically affect the success and evolutionary divergence of viruses. In the family Baculoviridae, two very different envelope fusion proteins have been identified. Budded virions of group I nucleopolyhedroviruses (NPVs) such as the Autographa californica multicapsid nucleopolyhedrovirus (AcMNPV), contain the essential GP64 envelope fusion protein. In contrast group II NPVs and granuloviruses have no gp64 gene but instead encode a different envelope protein called F. F proteins from group II NPVs can functionally substitute for GP64 in gp64null AcMNPV viruses, indicating that GP64 and these F proteins serve a similar functional role. Interestingly, AcMNPV (and other gp64-containing group I NPVs) also contain an F gene homolog (Ac23) but the AcMNPV F homolog cannot compensate for the loss of gp64. In the present study, we show that Ac23 is expressed and is found in budded virions. To examine the function of F protein homologs from the gp64-containing baculoviruses, we generated an Ac23null AcMNPV genome by homologous recombination in E. coli. We found that Ac23 was not required for viral replication or pathogenesis in cell culture or infected animals. However, Ac23 accelerated the mortality of infected insect hosts by approximately 28% or 26 h. Thus, Ac23 represents an important viral pathogenicity factor in larvae infected with AcMNPV.

SummaryThe development of wild-type Arabidopsis thaliana (L.) Heyhn and two lete-flowering fve mutants has been analysed under different environmental conditions. In wildtype plants, short-day photoperiods delay the floral transition as a consequence of lengthening all the developmental phases of the plant. Moreover, short days also alter the inflorescence structure by reducing the internode elongation and delaying the establishment of the floral developmental programme in the lateral meristems of the inflorescence and co-florescences. Mutations at the FVE locus cause a delay in flowering time, and a change in the inflorescence structure, similar to the effect of short photoperiods on wild-type plants. However, the effect of the fve mutations is additive to the effect of short days, and all the aspects of the Fve phenotype are corrected by vernalization. These results seem to indicate that FVE is not simply involved in timing the transition from vegetative to reproductive growth, but that it could play a role during all stages of plant development.

Message levels for a methionine-rich 10 kDa zein were determined in three inbred lines of maize and their reciprocal crosses at various stages during endosperm development. Inbred line BSSS-53, which overexpresses the 10 kDa protein in mature kernels, was shown to have higher mRNA levels in developing endosperm, as compared to inbred lines W23 and W64A. Differences in mRNA levels could not be explained by differences in transcription rate of the 10 kDa zein gene, indicating differential post-transcriptional regulation of this storage protein in the different inbred lines analyzed. Among progeny segregating for the BSSS-53 allele of the 10 kDa zein structural gene Zps10/(22), mRNA levels are independent of Zps10/(22) segregation, indicating that post-transcriptional regulation of mRNA levels takes place via a trans-acting mechanism. In the same progeny, mRNA levels are also independent of allelic segregation of the regulatory locus Zpr10/(22). Thus, the trans-acting factor encoded by Zpr10/(22) determines accumulation of 10 kDa zein at a translational or post-translational step. Multiple trans-acting factors are therefore involved in post-transcriptional regulation of the methionine-rich 10 kDa zein.

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The species Brassica oleracea includes several agricultural varieties characterized by the proliferation of different types of meristems. Using a combination of subtractive hybridization and PCR (polymerase chain reaction) techniques we have identified several genes which are expressed in the reproductive meristems of the cauliflower curd (B. oleracea var. botrytis) but not in the vegetative meristems of Brussels sprouts (B. oleracea var. gemmifera) axillary buds. One of the cloned genes, termed CCE1 (CAULIFLOWER CURD EXPRESSION 1) shows specific expression in the botrytis variety. Preferential expression takes place in this variety in the meristems of the curd and in the stem throughout the vegetative and reproductive stages of plant growth. CCE1 transcripts are not detected in any of the organs of other B. oleracea varieties analyzed. Based on the nucleotide sequence of a cDNA encompassing the complete coding region, we predict that this gene encodes a transmembrane protein, with three transmembrane domains. The deduced amino acid sequence includes motifs conserved in G-protein-coupled receptors (GPCRs) from yeast and animal species. Our results suggest that the cloned gene encodes a protein belonging to a new, so far unidentified, family of transmembrane receptors in plants. The expression pattern of the gene suggests that the receptor may be involved in the control of meristem development/arrest that takes place in cauliflower.

Using the meristems of the cauliflower curd as a source of tissue and a series of subtractive hybridizations and amplification reactions, we have constructed a cDNA library highly enriched in cDNAs expressed in reproductive meristems. The analysis of a sample of 250 clones from this library identified 22 cDNA clones corresponding to genes specifically expressed in these cauliflower meristems. Apart from two clones that corresponded to APETALA1, and two other ones showing similarity to different aminoacyl-tRNA synthetases, the remaining clones showed no similarity to any sequence in the databases and may correspond to novel genes. One of these clones, BoREM1, was further characterized and found to correspond to a gene encoding a protein with features of regulatory proteins that follows a expression pattern very similar to the LEAFY transcripts.

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A cDNA clone was isolated for Artemia salina protein HD40, a component of heterogenous nuclear ribonucleoproteins. Enriched Artemia 15S poly(A)+ RNA was used as a template and double-stranded cDNA sequences were inserted into the Pst I restriction endonuclease site of E. coli plasmid pBR322.RecombinanFtcolonies were analyzed by positivie hybri d selection of poly(A)+ RNA that directs the synthesis of protein HD40 in an in vitro assay. In vitro translation of the mRNA selected by recombinant cfoine87H yields a protein that is immunoprecipitated by anti-HD40 antibodies and that comigrates with authentic HD40 on gel electrophoresis. Partial proteolysis of protein HD40 and the in vitro translated product selected by clone 87HD produces the same peptideTpaTterns. The size of the cloned insert is about 820 bp. The length of HD40 mRNA as determined by Northern blot analysis, is about 1500 nucleotides. Southern blot analysis performed with DNA of different species (plant, avian, mnamnal) shows cross-hybridizing bands when probed with clone 87HD DNA suggesting that the HD40 gene is evolutionarily conserved. INTRODUCTIONIn eukaryotic cells, mRNAs and their nuclear precursors hnRNAs, are complexed with proteins giving rise to ribonucleoprotein particles (RNPs). The elucidation of the role of the proteins which bind RNA is essential for