FIG. 6.

Competition of tropoelastin mRNA degradation by exon 30. Polysomes and S100 extracts were isolated from two lines of neonatal lung fibroblasts (NLF-1 and -2) and two lines of adult lung fibroblasts (ALF-1 and -2) and were combined and incubated with (solid symbols) or without (open symbols) an excess of in vitro-transcribed exon-30 RNA. Samples were harvested, and mRNA levels for tropoelastin and GAPDH were assessed by RT-PCR. For tropoelastin mRNA, sequences coded by exons 35 and 36 were amplified. Tropoelastin mRNA in NLFs degraded with a half-life of ca. 6 h, and this rate was only minimally increased in the presence of exon-30 RNA. In contrast, tropoelastin mRNA degraded rapidly in ALFs with a half-life of less than 1 h and was essentially undetectable by 2 h. In the presence of excess exon-30 RNA, degradation of tropoelastin mRNA in ALF slowed but was nearly completely degraded by 7 h. The bottom panel shows the 2-, 5-, and 7-h ALF datum points graphed on an expanded y axis.