Multi-level regulation of lysosomal gene expression in lymphocytes

The expression of the gene coding for the lysosomal enzyme, beta-glucuronidase (Gus), was examined in functionally distinct T, B and plasma cell lines. Each of the different groups of cells had different intracellular levels of active Gus enzyme and numbers of Gus mRNA copies per cell. Analysis of the molecular forms of Gus mRNA and protein by Northern and Western blotting revealed that the different types of cells all produced a single mature 2.7 kb transcript and a 73 kDa polypeptide. However, the utilisation of the Gus mRNA to produce the Gus antigen, and the subsequent posttranslational processing of the polypeptide to generate the mature, enzymically active Gus, were found to be cell type-specific. Control of the functional expression of the Gus gene is thus exerted at both the transcriptional and translational levels, and appears to differ between different types of lymphocyte.