The E116 isolate of Dutch pea early-browning virus is a recombinant virus.

The complete nucleotide sequence of RNA2 of the E116 isolate of Dutch pea early-browning virus (PEBV-D) was obtained from overlapping cDNA clones. The RNA was found to encode three open reading frames corresponding to, in 5' to 3' order, the coat protein, the 2b nematode transmission protein and the C-terminal part of the cysteine-rich 1b protein derived from RNA1. The 3' non-coding region of PEBV-D RNA2 was also shown to be derived from RNA1. This is the first demonstration that recombination of PEBV occurs in nature. Comparison of the amino acid sequences of the PEBV-D RNA2 proteins with those of British PEBV and several isolates of tobacco rattle virus reveals complex patterns of mixing of the genomes of these two viruses.

Viral coat protein peptides with limited sequence homology bind similar domains of alfalfa mosaic virus and tobacco streak virus RNAs.

An unusual and distinguishing feature of alfalfa mosaic virus (AMV) and ilarviruses such as tobacco streak virus (TSV) is that the viral coat protein is required to activate the early stages of viral RNA replication, a phenomenon known as genome activation. AMV-TSV coat protein homology is limited; however, they are functionally interchangeable in activating virus replication. For example, TSV coat protein will activate AMV RNA replication and vice versa. Although AMV and TSV coat proteins have little obvious amino acid homology, we recently reported that they share an N-terminal RNA binding consensus sequence (Ansel-McKinney et al., EMBO J. 15:5077-5084, 1996). Here, we biochemically compare the binding of chemically synthesized peptides that include the consensus RNA binding sequence and lysine-rich (AMV) or arginine-rich (TSV) environment to 3'-terminal TSV and AMV RNA fragments. The arginine-rich TSV coat protein peptide binds viral RNA with lower affinity than the lysine-rich AMV coat protein peptides; however, the ribose moieties protected from hydroxyl radical attack by the two different peptides are localized in the same area of the predicted RNA structures. When included in an infectious inoculum, both AMV and TSV 3'-terminal RNA fragments inhibited AMV RNA replication, while variant RNAs unable to bind coat protein did not affect replication significantly. The data suggest that RNA binding and genome activation functions may reside in the consensus RNA binding sequence that is apparently unique to AMV and ilarvirus coat proteins.

Serological relationships and epitope profiles of isolates of okra leaf curl geminivirus from Africa and the Middle East.

A panel of seven murine monoclonal antibodies (mAbs) was raised against particles of okra leaf curl virus (OLCV), a whitefly-transmitted geminivirus which is prevalent in West Africa. The mAbs detected at least six distinguishable epitopes, two continuous and four discontinuous. In tests with these mAbs, relatively little antigenic variation was found among 24 OLCV isolates from Burkina Faso, Chad, Ghana, Ivory Coast, Nigeria, Oman and Saudi Arabia, each virus isolate reacting with at least five of them. However, on the basis of their reactions with 17 mAbs raised against particles of a group A isolate of African cassava mosaic virus (ACMV), the OLCV isolates could be assigned to two groups, which have geographical distributions that overlap in West Africa. A network of antigenic relationships was revealed by reactions between the OLCV mAbs and other whitefly-transmitted geminiviruses from six plant species in 12 countries. OLCV shared the most epitopes with tobacco leaf curl (African isolates) virus, ACMV, Indian cassava mosaic virus and bean golden mosaic virus. Selected OLCV mAbs are suitable for routine detection of OLCV, and a panel of three mAbs can be used to identify it.

Interacting genes in nematode dauer larva formation.

The dauer larva of Caenorhabditis elegans is a developmentally arrested stage induced by starvation or overcrowding. Mutant genes controlling the ability to form dauer larvae interact in a way which allows them to be ordered in a pathway. Mutant phenotypes suggest that the pathway corresponds to neural processing of environmental stimuli.

The shibire(ts) mutant of Drosophila: a probe for the study of embryonic development.

A temperature-sensitive mutant strain (shibire) has been used to probe the normal developmental process in Drosophila melanogaster. At high temperatures lethality occurs during embryonic development. Heat pulses given early disrupt cellular blastoderm formation in these mutants. Even in the absence of cells, the embryo begins morphogenetic movements characteristic of gastrulation. With heat pulses given later, the embryonic cells proliferate without normal differentiation.