Abstract: Expression vector for expressing the E. coli a polypeptide other than E. coli malate dehydrogenase coded for by a DNA coding sequence. The vector includes a DNA coding for the polypeptide and also includes an initiation codon wherein the DNA sequence is operatively linked to an upstream sequence located upstream of the initiation codon and which is capable of controlling expression of the polypeptide. The upstream sequence consists on the 285 base pair sequence defined by SEQ ID NO:3. A process for expressing a polypeptide by culturing a host strain of E. coli transformed with an expression vector of the invention is also provided.

Abstract: Apparatus for optical analysis of particles such as biological cells utilizes twin beams passing through a common optical fibre to avoid problems of alignment. For scattering measurements, a narrower beam can be used to gate detection of a broader beam to avoid amiguities associated with off-axis particles. The twin beams can also be used for thermal lensing, fluorescence or other techniques. Different beam diameters can alternatively be achieved in a single beam by controlling the focal length of a beam focussing lens.