THE ANTITERMINATOR RNA OF PHAGE-HK022

The put sites of phage HK022 increase the processivity of transcriptio n and thereby promote the expression of viral genes that are located d ownstream of transcription terminators. RNA polymerase molecules that have traversed a put site are converted to a terminator-resistant form by the put transcript. We analyzed the structure and function of put transcripts by determining the effects of put mutations on terminator read-through, and by probing wild-type and mutant put RNAs with struct ure-specific nucleases. The results support the prediction that the se condary structure of the active transcript consists of two hairpin ste ms that are separated by a single unpaired base. The identity of bases in certain bulges and internal loops is important for activity, while that of most bases in the terminal loops is not. Many bases in the st ems can be replaced with little or no effect on activity provided that base-pairing is maintained. (C) 1997 Academic Press Limited.