The causes of the aberrant constitutive expression of cytokines in SLE have not been elucidated yet, but alterations in cytokine gene structure could be a contributing factor. By RFLP (Restriction Fragment Length Polymorphism) analysis of genomic DNA, we found a higher incidence of allelic, higher MW XbaI bands in the IL-6 genes of 9/57 SLE patients vs 1/36 unrelated controls (p = 0.05) HLA DR/DQ typing of the polymorphic patients revealed they were all DQ beta 6. The study of one family indicated that the XbaI polymorphic patient and her polymorphic unaffected offspring had higher than normal levels of constitutive IL-6 mRNA. The SLE-associated IL-6 XbaI restriction alleles had duplications of AT-repeat sequences, approximately 500 bp downstream of the 2nd polyadenylation site, in an AT-rich mini-satellite with similarities to Matrix Associated Regions (MARs), that may be important in DNA replication and in gene expression. These are novel observations that suggest that, in SLE, there is increased variability in the 3' flanking region of the IL-6 gene. This variability may be related to the aberrant IL-6 expression that was reported by us and others in this disease.

Aims: To construct expression vectors capable of switching promoters under different metabolic circumstances to obtain stable gene expression. Methods and Results: In this study, we designed a series of constructs for the expression of the chicken lactate dehydrogenase (cldh) gene under the control of galactose-inducible GAL1 promoter and the high glucose-inducible HXT1 promoter in Saccharomyces cerevisiae. In one construct, the HXT1 promoter was placed between artificial splicing sequences to function as an intronic promoter. We checked all constructs for the usage of promoters by reverse transcriptional polymerase chain reaction and assayed the expression level of the reporter gene under different culturing conditions. In the presence of galactose, when the GAL1 promoter was linked with the intronic HXT1 promoter, the cldh gene showed 1AE5-fold activity compared with single GAL1 promoter, while in the presence of glucose, the construct showed over twofold activity compared with that without splicing sequences. Conclusion: The intronic HXT1 promoter could be induced by the presence of high glucose concentration. Significance and Impact of the Study: This is the first report detailing the use of an intronic promoter in the construction of stable expression vectors and the novel system could serve as a model of expression vectors for fermentation or other purposes.