TheAzotobacter vinelandiichromosome

The chromosome ofAzotobacter vinelandiiwas digested with the restriction endonucleasesSpeI (5’-ACTAGT),DraI (5’-TTTAAA) andAsel(5’-ATTAAT) and the products were separated by pulsed-field gel electrophoresis. The sum of the sizes of the restriction fragments comes to around 4.5 megabasepairs. Our earlier studies had revealed the presence of about 80 copies ofnifH, nifD, nifKandleuBgenes in a log-phase cell ofA. vinelandii.To determine whether there are multiple identical chromosomes inA. vinelandiior one large chromosome with identical segments joined in tandem, we have subjected gamma-irradiated DNA ofA. vinelandiiandEscherichia colito pulsed-field gel electrophoresis. The results suggest thatA. vinelandiichromosomes contain multiple identical chromosomes of about the same size as that ofE. coli.