Adenoviruses express up to 20 distinct mRNAs from five major late transcription unit (MLTU) regions, L1 to L5. The L4 region expresses L4-33K and a related protein, L4-22K [1]. L4-22K and L4-33K have complementary but not redundant functions that provide the normal pattern of mRNA production during the late phase of infection [1]. L4-33K is an alternative RNA splicing factor that up-regulates several MLTU splice acceptor sites as the late phase progresses [1,2]. L4-22K plays a role in genome packaging via its binding, in association with IVa2, to the A2 sequence within the packaging signal [3]. Additionally, L4-22K plays an important role in the temporal switch from the early to late phase of infection by regulating both early and late gene expression [4,5].

1: Adenovirus serotype 5 L4-22K and L4-33K proteins have distinct functions in regulating late gene expression. Morris SJ, Leppard KN; J Virol. 2009;83:3049-3058. PMID:19176628

2: L4-33K, an adenovirus-encoded alternative RNA splicing factor. Tormanen H, Backstrom E, Carlsson A, Akusjarvi G; J Biol Chem. 2006;281:36510-36517. PMID:17028184

3: The L4 22-kilodalton protein plays a role in packaging of the adenovirus genome. Ostapchuk P, Anderson ME, Chandrasekhar S, Hearing P; J Virol. 2006;80:6973-6981. PMID:16809303

4: Decreased activity of Reiter's syndrome after urethrectomy. Rubin RA, Goldfarb RA, Lidsky MD, Abrams J; Arthritis Rheum. 1990;33:885-887. PMID:2363740

5: The adenovirus L4-22K protein is multifunctional and is an integral component of crucial aspects of infection. Wu K, Orozco D, Hearing P; J Virol. 2012;86:10474-10483. PMID:22811519