Abstract: The problem of diagnosis and typing of infectious bronchitis virus in poultry has been solved and important progress made towards an IBV vaccine by this invention. DNA complementary to the region of genomic IBV RNA which codes for a spike protein polypeptide comprising the S1 polypeptide (containing antigenic determinants) or the S2 polypeptide (containing means for anchoring the spike protein to the viral membrane) has been made. It can be carried by a cloning vector, incorporated in a host and cloned. It can also be cloned in a poxvirus which is used to transfect mammmalian cells. Such cells express an artificial spike protein polypeptide.

Abstract: The invention discloses that, in the presence of NifA and NtrA, the expression of a desired DNA molecule which has been operably linked to an ntrA-RNA polymerase and NifA dependent promoter can be regulated by regulating the oxygen level of the culture medium. The invention relates to vectors which may be used in accordance with this discovery, and to methods for using such vectors.