ABSTRACT
Considerable progress in the molecular analysis of symbiotic nitrogen fixation, achieved within the last few years, is directly related to advances in methods of recombinant DNA technology, generally suitable for Gram-negative bacteria. Essential for such analytical studies is the availability of versatile cloning and vector systems. Mutants arise spontaneously with low probability or may be obtained by treatment with chemical or physical mutagens. However, the alternative, transposon mutagenesis, offers major advantages compared to these classic procedures. There are two ways of generating fusions, depending on the transposon used and they are: Translational fusion, Transcriptional fusion. The most widely used indicator gene is the lacZ gene of E. coli which specifies the enzyme ß-galactosidase. The basic idea of combining in one replicon both narrow host-range maintenance functions and interspecific transfer proficiency has been realized by cloning transfer genes from different sources into E. coli specific vector plasmids.
