The intron requirement for immunoglobulin gene expression is dependent upon the promoter.

Transfection assays were used to assess the need for an intron in order to obtain expression of cytoplasmic immunoglobulin mu mRNA. An intron is required when transcription is driven by an immunoglobulin promoter/enhancer combination, although this requirement is not specific for a particular intron. However, this need for an intron is dependent upon the promoter used. Whilst an intron is required in the case of immunoglobulin or beta-globin promoters, it is not in the case of cytomegalovirus or heat-shock promoters. The data point to a connection between the promoter and RNA processing or export.