Cloning and expression of fragment of the rabies virus nucleoprotein gene in Escherichia coli and evaluation of antigenicity of the expression product

Rabies virus nucleoprotein (N protein) encapsidates genomic RNA of the virus and forms the viral ribonucleoprotein complex. These N proteins represent highly organized structures which activate proliferation of B cells and production antibodies against the N protein. In addition to the B cell, the rabies virus N protein has been shown to induce potent T helper cell responses resulting in a long-lasting and strong humoral immune response. Rabies virus N protein is a molecular target of choice for development of tools to diagnose acute rabies infection. We produced a recombinant immune reactive C-terminal fragment of the rabies virus N protein which contains an antigenic determinant located between positions 360-389. Synthetic gene encoding the N protein was cloned into an expression plasmid to produce the recombinant antigen in Escherichiacoli cells BL21 (DE3). SDS-PAGE showed presence of the product with expected molecular weight (44 kDa). The recombinant fragment of the N protein efficiently recognized antibodies in sera from mice immunized with an inactivated rabies virus. Thus produced recombinant antigen of the rabies virus N protein can be used in an enzyme-linked immunosorbent assay (ELISA) for diagnosis of the rabies infection.

Mutations in the pncA and rpsA genes among 77 Mycobacterium tuberculosis isolates in Kazakhstan

SETTING

Pyrazinamide (PZA), an important first-line drug for anti-tuberculosis treatment, demonstrates potent activity against semi-dormant bacilli in acidic environments. However, the diagnosis of PZA resistance is often impeded by technical difficulties.

OBJECTIVE

To characterise mutations in the pncA and rpsA genes among PZA-resistant and PZA-susceptible clinical Mycobacterium tuberculosis isolates circulating in Kazakhstan. The potential use of genotyping to identify PZA resistance was also investigated.

DESIGN

PZA drug susceptibility testing and pncA and rpsA gene sequencing were performed on 77 clinical M. tuberculosis isolates; mycobacterial interspersed repetitive unit-variable number tandem repeat (MIRU-VNTR) typing was performed on 74 clinical M. tuberculosis isolates.

RESULTS

Of the 77 clinical M. tuberculosis isolates, 41 (53.2%) were phenotypically resistant to PZA, whereas 36 (46.7%) were susceptible; 48 (62.3%) of these isolates were also multidrug-resistant (MDR). Furthermore, 38 (49.3%) clinical isolates showed mutations in the pncA gene and its flanking region; the majority of these isolates (n = 36, 94.7%) were also MDR. Gene sequencing showed that only synonymous substitutions affecting rpsA occurred. MIRU-VNTR typing revealed that 78.4% of isolates were of the Beijing genotype.

CONCLUSIONS

Sequencing revealed that mutations in pncA, but not in rpsA, occurred in PZA-resistant M. tuberculosis isolates circulating in the territory of Kazakhstan.

An ancient player unmasked: T4 rI encodes a t-specific antiholin

Phage T4 effects lysis by its holin T and its endolysin E. Lysis is inhibited (LIN) if the infected cell is subjected to secondary infections by T4 phage particles. The T4 rI gene is required for LIN in all hosts tested. Here, we show that a cloned rI gene can impose a T-specific LIN on T-mediated lysis in the context of the phage lambda infective cycle, in the absence of other T4 genes and without secondary infection by T4. Moreover, it is shown that the T holin accumulates in the membrane during LIN, forming SDS-resistant oligomers. We show by cross-linking experiments that a T-RI heterodimer is formed during LIN, demonstrating that RI belongs to the functional class of antiholins, such as the S107 protein of lambda, which heterodimerizes with its cognate holin, S105. Finally, we show that the addition of Ni(2+) ions to the medium can block lysis by a T protein hexahistidine-tagged at its C-terminus, suggesting that liganding of the periplasmic domain is sufficient to impose lysis inhibition. The results are discussed in terms of a model in which the LIN-inducing signal of the secondary infecting phage influences a conformational equilibrium assumed by RI in the periplasm.

Functional analysis of the phage T4 holin in a lambda context

Phage lambda hybrids were constructed by inserting the t gene of phage T4 in place of the lambda holin gene, S. Induction of the hybrid phage resulted in lysis that was just as abrupt as, but occurred much earlier in the vegetative cycle than, that obtained with lambda, indicating that t is indeed a holin gene. Moreover, it was possible to impose lysis inhibition (LIN) on induction of the hybrid phage, but not of the parental lambda phage, by superinfection with LIN-competent T4. The imposition of the LIN state was found to depend on the allelic state of the rI and t genes of the superinfecting T4 phage, indicating that the LIN-sensitive state of the T holin is transient. Finally, induction of lysogens carrying both holin genes was shown to result in earlier triggering of lysis than with either holin gene alone. This result suggests that the two very dissimilar holins contribute additively to the physiology of the timing mechanism, or, less likely, that they interact to form one mass-action pool. In either case, these results imply a common pathway for holin timing and function.

Genetic analysis of the T4 holin: timing and topology

The t protein of bacteriophage T4 shares with other holins the ability to cause the formation of a lethal membrane lesion which allows the phage endolysin to attack the peptidoglycan. Moreover, T, like other holins, acts in a saltatory manner at a precisely programmed time in the vegetative cycle. Unlike other holins, however, T has the unique ability to postpone its lethal function in response to a secondary infection by a T-even phage during the vegetative cycle. A signal transduction system that responds to the secondary infection is thought to be encoded by some of the numerous r genes, defined by mutations that abolish this lysis-inhibition (LIN) response. The primary structure of T differs from two main structural patterns found in more than 30 orthologous groups of holins. Genetic approaches were taken to probe the t sequence for features involved in membrane localization, functional timing and LIN regulation. Gene fusion analysis indicates that T has a single TMD near the N-terminus, with the bulk of the protein residing in the periplasm. Mapping and phenotypic analysis of deletion and point mutations in t indicates that the periplasmic domain of T is the major determinant of the timing mechanism and is involved in the LIN response.