Processive antitermination can be mediated by RNA as well as proteins. Coliphage HK022, alone among the known lambdoid phages, does not encode an analog to lambda N. Instead, it promotes antitermination of early phage transcription through the direct action of transcribed sequences called "put" (for polymerase utilization) sites. There are two closely related "put" sites, one located in the PL operon and the other located in the PR operon, roughly corresponding to the positions of the "nut" sequences in lambda and in other lambda relatives. "put" sites act in cis to promote readthrough of downstream terminators in the absence of all HK022 proteins. The "put" transcripts are predicted to form two stem-loops separated by a single unpaired nucleotide. This prediction is supported by mutational studies and the pattern of sensitivity of the two RNAs to cleavage with single- and double-strand-specific endoribonucleases. RNA structure is critical to antitermination because mutations that prevent the formation of base pairs in the stems reduce function, and these mutations can be suppressed by additional mutations that restore base pairing. Like lambda N and Q, the "PUT" sequences suppress polymerase pausing and promote processive antitermination in a purified in vitro transcription system. In contrast to lambda N, no phage or auxiliary bacterial factors are required. The only mutations known to block "PUT"-mediated antitermination change highly conserved amino acids located in a cysteine-rich amino-proximal domain of the RNAP beta' subunit. Strains carrying these mutations are unable to support lytic growth of HK022 but are normal in all other respects tested, including lytic growth of lambda and other lambda relatives. The phage-restricted phenotypes conferred by these mutations suggest that they alter a domain of RNAP-beta’ that interacts specifically with nascent "PUT" RNA in the transcription elongation complex, but this idea has not been directly tested. The stability of the putative "PUT"-RNAP interaction and the nature of the "PUT"-induced modification to the elongation complex are unknown.