Transcription of human type I collagen genes. Variation in the relative rates of transcription of the pro alpha 1 and pro alpha 2 genes.
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abstract
The relative rates of transcription of the two genes for type I collagen have been measured in a runoff transcription assay using nuclei isolated from cultured human fibroblasts. Control experiments indicated that the ratio of pro alpha 1(I)/pro alpha 2(I) transcripts detected with a given nuclear preparation did not vary over a range of transcription times, nuclei concentrations, and amounts of filter-bound cDNA used in the assay. However, a significant difference in the ratio was observed when nuclei isolated from cells grown under different conditions were used. Nuclei from sub-confluent cultures generally transcribed the two genes in a ratio of 2:1 or lower, while nuclei from post-confluent cultures transcribed the genes in a much higher ratio of about 4:1. Analysis of the amount of pro alpha 1(I) and pro alpha 2(I) RNA transcribed suggests that it is the transcription of the pro alpha 1(I) gene, and not the pro alpha 2(I) gene, that varies with culture conditions. The steady state ratios of pro alpha 1(I)/pro alpha 2(I) RNA remained near 2:1 under all conditions. Thus, some post-transcriptional mechanism apparently results in maintenance of the steady-state pro alpha 1(I)/pro alpha 2(I) RNA ratios at approximately 2:1.
