first cyclin box found in transcription factor IIIB 90 kDa subunit (TFIIIB90) and similar proteins
TFIIIB90, also called B-related factor 1 (BRF-1), or TATA box-binding protein-associated factor, RNA polymerase III, subunit 2 (TAF3B2), is a general activator of RNA polymerase which utilizes different TFIIIB complexes at structurally distinct promoters. TFIIIB90 contains two cyclin boxes. This model corresponds to the first one. The cyclin box fold is generally a protein binding domain, but binds DNA in TFIIIB90.
Jiyao W et al.(2023). "The conserved domain database in 2023.",