Abstract: A method for identifying an essential gene of an organism, which method comprises: (i) providing a library of transposon insertion mutants of the said organism, wherein the transposon comprises an RNA polymerase recognition sequence; (ii) isolating chromosomal DNA from the library of (i), (iii) digesting the chromosomal DNA with a restriction endonuclease that is capable of cutting 5′ of the RNA polymerase recognition site in the transposon and 3′ of the RNA polymerase recognition site in the chromosomal DNA flanking the transposon; (iv) self-ligating the digested DNA, (v) amplifying the self-ligated DNA by inverse PCR (iPCR), (vi) transcribing RNA from the amplified DNA, (vii) hybridising the transcribed RNA with an oligonucleotide array; and (viii) identifying a probe on the oligonucleotide array which corresponds to an essential gene of the organism.

Abstract: A fusion protein suitable for use as a vaccine comprises an amino acid sequence having biological activity which is fused via an intervening hinge comprising from two to eight glycine-proline repeats to the C-terminus of sufficient of the amino acid sequence of a B subunit of an enterotoxin which is capable of ADP-ribosylation of a GTPase.

Abstract: The invention concerns a vaccine comprising an attenuated Salmonella bacterium which contains a nirB promoter operably linked to a DNA sequence encoding a heterologous protein. The nirB promoter directs expression of the heterologous protein in a host it is wished to vaccinate.

Abstract: A process for the preparation of a protein, which process comprises culturing under such conditions that the protein is obtained cells infected with a recombinant baculovirus having a promoter, capable of directing the expression of a gene in the cells, operably linked to a heterologous gene which encodes the protein and which is preceded by a leader sequence comprising: T A A T C A T C C A C A G G A G A C T T T C T G [SEQ. ID NO: 1].