HMGA1a is involved in specific splice site regulation of human immunodeficiency virus type 1

► A human host protein, HMGA1a is involved in specific splice site regulation of HIV-1. ► HMGA1a binds a sequence adjacent 5′ splice site 3 (D3) and induces incomplete pre-mRNA splicing which is necessary for HIV-1 related Vpr mRNA production. ► This is the first example of a non-classical splicing factor (non-SR, non-hnRNP factor) to regulate alternative splicing of HIV-1.