The Streptomyces coelicolor sporulation-specific sigma WhiG form of RNA polymerase transcribes a gene encoding a ProX-like protein that is dispensable for sporulation

In the non-motile mycelial organism Streptomyces coelicolor A3(2), the sporulation gene whiG encodes a protein that closely resembles RNA polymerase sigma factors such as sigma D of Bacillus subtilis, which mainly control motility and chemotaxis genes. Here, we show that the whiG gene product, purified from an Escherichia coli strain carrying an expression construct, could activate E. coli core RNA polymerase in vitro to transcribe a sigma D-dependent motility-related promoter from B. subtilis. Such RNA polymerase holoenzyme preparations could also transcribe from an S. coelicolor promoter, PTH4, previously shown to require an intact whiG gene for in-vivo transcription. The in-vivo dependence on whiG was therefore shown to be direct. Unusually, the initiation of PTH4 transcription in vitro depended on the provision of appropriate dinucleotides. The whiG-dependent PTH4 transcription unit consisted of a single gene, orfTH4. Sequence comparisons suggested that the gene product was a member of a small group of proteins that include the B. subtilis and E. coli ProX proteins. Though none of these proteins shared more than about 30% of extended primary sequence identity, they had similar size and hydropathy profiles, and could be aligned end to end to reveal a mosaic of similarities. The ProX proteins of B. subtilis and E. coli are implicated in glycine betaine transport in response to hyperosmotic stress. However, disruption of orfTH4 did not cause any obvious phenotypic changes in growth or development on media of varying osmotic strengths.

Analysis of the genetic variability of maize streak virus

The nucleotide sequences of the small intergenic region (SIR) and the gene encoding the coat protein of 12 maize streak virus (MSV) isolates from different geographic locations have been determined. These have been used to assess the variability of the virus and to construct evolutionary dendrograms. For the viruses analyzed, the maximum levels of sequence divergence were found to be 10.9% and 2.0% at the nucleotide and amino acid levels, respectively. A genetically distinct strain of MSV was collected from islands in the Indian ocean. The significance of these findings for detection of the virus in epidemiological studies and breeding of resistant plant varieties is discussed.

Rapid production of full-length, infectious geminivirus clones by abutting primer PCR (AbP-PCR)

The application of the polymerase chain reaction (PCR) method of DNA amplification for the isolation of full-length, infectious clones of geminiviruses is described. Non-overlapping, abutting 20-mer oligonucleotide primers were used to produce a linear product from the circular geminivirus genomic template. Clones of African cassava mosaic virus (ACMV) DNA A, obtained by this method, were infectious following mechanical inoculation (in the presence of ACMV DNA B) onto Nicotiana benthamiana. Normal ACMV symptoms resulted and typical geminate viral particles were detected by electron microscopy. The use of PCR for the detection and production of full-length, infectious geminivirus clones is discussed.

The nucleotide sequence of an infectious insect-transmissible clone of the geminivirus Panicum streak virus

The infectious genome of a Kenyan isolate of Panicum streak virus (PSV) has been cloned and sequenced. Infection of host plants was done using an Agrobacterium binary vector containing a partial repeat of the genome. Progeny virus from resultant infections proved to be transmissible by the leafhopper Cicadulina mbila (Naude). Comparisons of the amino acid sequences of PSV DNA-encoded proteins with those of previously characterized geminiviruses infecting monocotyledonous plants, including maize streak virus, revealed high levels of identity. The evolutionary relationship between PSV and other geminiviruses infecting monocotyledons is discussed.