Abstract Alginate gel-entrapped cells of auxotrophic thymine-dependent strain of E. coli catalyze the transfer of 2-deoxy-D-ribofuranosyl moiety of 2'-deoxyuridine to purine and pyrimidine bases as well as their aza and deaza analogs. All experiments invariably gave β- anomers; in most cases, the reaction was regiospecific, affording N 9-isomers in the purine and N 1-isomers in the pyrimidine series. Also a 2, 3-dideoxynucleoside can serve as ...