GENE-SPECIFIC MODULATION OF RNA-SYNTHESIS AND DEGRADATION BY EXTREMELY-LOW-FREQUENCY ELECTROMAGNETIC-FIELDS

Pulse-labeling studies from our laboratory and others have shown that extremely low frequency (ELF) electromagnetic fields can produce a tra nsient increase in gene transcription. In this study, the synthesis, d egradation and processing, and steady state levels of specific RNA spe cies during exposure to ELF radiation were determined in human leukemi a HL-60 cells. The overall steady state RNA levels, assessed by contin uous and equilibrium labeling with H-3-uridine, were not affected by E LF exposure. Northern blot analysis using probes specific for c-myc, b eta-actin, and 45S ribosomal RNA gene products revealed that ELF did n ot alter the steady state levels of these RNAs. Examination of gene-sp ecific transcription by a novel nuclease protection assay revealed tha t while ELF did not substantially alter the transcription rates for c- myc and beta-actin, transcription of the 45S ribosomal RNA gene was in creased by 40-50%. To explain the observed increase in the synthesis o f 45S ribosomal RNA without an associated increase in its steady state level, the degradation and processing of the ribosomal gene transcrip t in the presence and absence of an ELF field were followed by pulse-c hase H-3-uridine labeling. This revealed that ELF radiation accelerate d both the processing and degradation of the ribosomal RNA transcript. During ELF exposure, the half-life of the 45S ribosomal RNA was decre ased from 115 min. to 85 min. These results show that ELF can selectiv ely affect RNA levels by modulating either the transcription rate and/ or RNA post-transcriptional processing and turnover,