Production of human papillomavirus type 16 major capsid protein L1 in undifferentiated cells is negatively regulated by several yet unidentified cis-acting inhibitory RNA elements, among which a major element is located within the first 514 nucleotides of the L1-mRNA. By Northern blotting we examined effect of the major element on the steady-state level of mRNA transiently transcribed in 293T cells from the firefly luciferase (Fluc) gene combined with the L1 DNA fragment encoding the major element. As reported previously, the element down-regulated steady-state level of the mRNA. The most efficient down-regulation was achieved by insertion of the element near the 5' end of mRNA, resulting in an undetectable level of the mRNA. The longer the distance from the 5' end of the mRNA to the element, the weaker the down-regulation. The half-life of the mRNA having the element was similar to that of normal Fluc-mRNA. When the element near the 5' end was removed by splicing, the steady-state level of the resultant mRNA was raised to a readily detectable level. The steady-state level of RNA synthesized by RNA polymerase-I was not influenced by the presence of the element. Taken together, it is suggested that DNA region encoding the major inhibitory element does not disturb transcription and that the pre-mRNA is degraded by an RNA element-mediated mechanism after the splicing step in the course of mRNA maturation.