Analysis of the motA flagellar motor gene from Rhodobacter sphaeroides a bacterium with a unidirectional, stop-start flagellum

Rhodobacter sphaeroides swims by unidirectional rotation of a single medial flagellum, re-orienting randomly by Brownian motion when flagellar rotation tops and restarts. Previously we identified a mutant with a paralysed flagellum, which was complemented by a Rhodobacter gene that had homology to motB of Escherichia coli , a bacterium with bidirectional flagella. In the current work, interposon mutagenesis upstream of the Rhodobacter motB gene gave rise to another paralysed mutant, RED5. DNA sequence analysis of this upstream region showed one open reading frame, the predicted polypeptide sequence of which shows homology to the MotA protein of E. coli . MotA is thought to be a proton 'pore' involved in converting proton-motive force into flagellar rotation. Several potential proton-binding amino acids were conserved between putative membrane-spanning regions of R. sphaeroides and E. coli MotA sequences, along with a highly charged cytoplasmic linker region. Complementation studies with mutant RED5 showed the presence of an active promoter upstream from motA which was found to be necessary for expression of both motA and motB , Examination of the upstream DNA sequence showed only one putative promoter-like sequence which resembled a σ⁵⁴- type promoter, including a potential enhancer binding site. The overall similarities between the R. sphaeroides MotA protein and those from other bacteria suggest that, despite the novel unidirectional rotation of he R. sphaeroides flagellum, the function of the MotA protein is similar to that in bacteria with bidirectional flagella.     

One short well conserved region of Alu-sequences is involved in human gene rearrangements and has homology with prokaryotic chi.

Alu elements have repeatedly been found involved in gene rearrangements in humans. Although these elements have been suggested to stimulate gene rearrangements, sparse information is available for the possible mechanism(s) of these events. Here we present a compilation of Alu elements that have been involved in recombinational events leading to gene rearrangements, indicating the presence of a common 26 bp core sequence at or close to the sites of recombination. Besides the obvious possibility of retrotransposition, gene rearrangements may be induced by sequences that stimulate genetic recombination. We suggest that the core sequence stimulates recombination and may thereby cause the frequent involvement of these elements in gene rearrangements. Curiously, the core sequence contains the pentanucleotide motif CCAGC, which is also part of chi, an 8 bp sequence known to stimulate recBC mediated recombination in Escherichia coli.     

Analysis of the sequence of a new cryptic plasmid, pRJF2, from a rumen bacterium of the genus Butyrivibrio: Comparison with other Butyrivibrio plasmids and application in the development of a cloning vector

Abstract A small cryptic plasmid, pRJF2, from Butyrivibrio fibrisolvens strain OB157 was isolated and sequenced. The plasmid is similar in organisation to the previously sequenced Butyrivibrio plasmid, pRJF1, with two open reading frames, ORF1 and ORF2, flanking a region tentatively identified as the replication origin, and a region of unknown function defined by terminal 79 bp invert repeats. The sequences of ORF1, ORF2, and the presumptive replication origin are highly conserved. The sequence between the 79 bp invert repeats is not, and is therefore presumed to be of lesser functional significance, although the 5' and 3' termini are still highly conserved. The functional importance for plasmid replication of these regions was tested by constructing potential shuttle vectors, each lacking one or more of the regions of interest. When the region between the invert repeats was deleted and replaced by the erythromycin resistance gene from pAM β1 together with pUC18, to produce the 7.9 kb chimaeric plasmid pYK4, the construct was successfully transformed into E. coli and B. fibrisolvens by electroporation, and was stably maintained in both hosts. Both ORF1 and ORF2 were required for successful transformation of B. fibrisolvens .     

Malignant transformation of rat thyroid cells transfected with the human TSH receptor cDNA.

Growth and function of well differentiated FRTL-5 thyroid cells depend on thyrotropin as its main regulatory hormone. We demonstrate here that stable transfection of FRTL-5 cells with the human thyrotropin receptor cDNA results in cellular transformation of these cells with altered cell shape and loss of contact inhibition. The transformed cells replicate in soft agar and form invasive tumors when cell suspensions are implanted onto nude mice. They have lost their thyrotropin dependent growth and their ability to concentrate iodide and synthesize thyroglobulin. But they still express the rat thyrotropin receptor mRNA and accumulate cAMP in response to thyrotropin stimulation. However, although the full length human thyrotropin receptor cDNA is integrated into their genome, transformed cells do not express the human thyrotropin receptor mRNA.