Modification of mRNA secondary structure and alteration of the expression of human interferon alpha 1 in Escherichia coli

A plasmid (pNL015) was constructed to contain a human interferon alpha 1 (IFN-alpha 1) gene under the transcriptional control of the Escherichia coli lipoprotein promoter. The E. coli cells harboring this plasmid produce 2.8 x 10(4) units/ml of IFN. Secondary structure analysis of the transcripts produced by pNL015 showed that the coding region could base pair with the Shine-Dalgarno (SD) region with a delta G = -3.9kcal/mol. A new plasmid pNL008 was constructed by modifying pNL015 with an 11-bp deletion and a 2-bp insertion in the coding region, so that the SD region is not involved in the secondary structure. E. coli cells harboring pNL008 produce ten times more IFN activity than cells harboring pNL015. A series of experiments were carried out to show that the specific activities of IFN, differential rates of IFN transcription, protein degradation or mRNA degradation could not account for the difference observed in expression. A rigorous test on this model of translational inhibition was conducted by the construction of pNL017 with a single bp substitution which did not change the amino acid sequence of the IFN (synonymous codon substitution) but which increased the calculated energy of interaction with the SD sequence to delta G = -10.8 kcal/mol. The E. coli cells harboring pNL017 produced no detectable IFN activity.

Arylsulfatase in natural killer cells: its possible role in cytotoxicity

Ultrastructural cytochemistry of natural killer cells enriched by Percoll gradient centrifugation showed them to possess arylsulfatase (aryl-sulfate sulfohydrolase, EC 3.1.6.1). The enzyme was located in vesicles, granules, and the parallel tubular arrays, organelles characteristic for cytotoxic lymphocytes. Biochemically, peak enzyme activity correlated with the Percoll fractions containing cells with cytotoxicity for melanoma target cells. Treatment of natural killer cells with Na2SO4, a competitive inhibitor of arylsulfatase, suppressed cytotoxicity by almost 50%. Electron microscopy of effector-target cell conjugates, which had been permitted to incubate for only 30 min, disclosed numerous arylsulfatase-positive sites at the points of contact between the effector/target cell membranes. Thus, the enzyme was translocated to the surface before lysis of the target cell was morphologically evident. It is postulated that the parallel tubular arrays play a role in this translocation and that arylsulfatase may function in the degradation of cerebroside sulfate ester components of the target cell membrane to initiate the lytic event.