All RNA polymerases III terminate transcription at extremely simple sites, consistent with their role in producing small transcripts. These sites are essentially "Tn" (in the non-transcribed strand). Termination signals are recognized directly by polymerase III (Bogenhagen and Brown, 1981; Cozzarelli et al., 1983; Hamada et al., 2000). In vitro, hs sp and scpol III terminate transcription with comparable efficiency at T4, T4-5, and T5-6, respectively (Allison and Hall, 1985; Hamada et al., 2000; Huang and Maraia, 2001). At T runs that are sufficiently short to yield incomplete termination, nearby sequence influences the efficiency of termination (Bogenhagen and Brown, 1981; Gunnery et al., 1999; Mazabraud et al., 1987). The pol III termination site is a strong pause site; elongating transcription complexes that eventually read through a terminator do so with a significant time delay. This is in keeping with readily detectible slowing of RNA chain elongation by scpol III that is generated by even short runs of U incorporation into RNA (such as sequence found in U3) (Matsuzaki et al., 1994).

Termination of transcription by scpol III is associated with repetitive hydrolytic resection of the nascent RNA chain's 3' end and resynthesis, an activity that requires the C11 subunit of pol III. In the absence of C11, pausing during transcript elongation is greatly reduced and RNA chain termination is severely but not absolutely defective. In such a case accurate termination (and RNA chain release) is restored at extremely low concentrations of UTP (1 and 3 μM). C11 is proposed to exert its effect on termination indirectly by increasing RNA pausing. By increasing the time spent at the terminator the probability of read-through is decreased. This is different from the C11 subunit's direct RNase activity during hydrolytic RNA chain retraction (Chédin et al., 1998).