A gene encoding 1-aminocyclopropane-1-carboxylate (ACC) synthase produces two transcripts: elucidation of a conserved response.
Indole-3-acetic acid (IAA) promotes ethylene biosynthesis in stems of etiolated pea (Pisum sativum L.) seedlings by rapidly increasing the expression of 1-aminocyclopropane-1-carboxylate (ACC) synthase mRNA and by enhancing the activity of the enzyme. Two cDNA clones encoding ACC synthase, Ps-ACS1 and Ps-ACS2, were isolated from a cDNA library prepared from the apical hooks of etiolated pea seedlings that had been treated with 100 microns IAA for 4 h. While studying the expression pattern of IAA-induced ACC synthase mRNA, we observed that the probe for Ps-ACS1 hybridized to two transcripts of 1.6 and 1.9 kb on RNA gel blots. The shorter transcript accumulated before the longer one did, indicating that it is not a degradation product of the latter. Because a similar observation, namely hybridization of one ACC synthase probe to two transcripts, has also been reported in other species, we investigated the relationship between the 1.6- and 1.9-kb transcripts. DNA gel blot analysis using the entire cDNA as probe and RNA gel blot analysis using the 3'-untranslated region as probe indicated that both transcripts are encoded by the same gene. Oligonucleotide-directed RNase H mapping showed that the transcripts differ in the sequence of their 5'-ends. Using 5'-RACE to obtain the DNA sequence of the shorter, transcript, we determined that the 1.6-kb transcript (Ps-ACS1b) begins within the second exon of the 1.9-kb transcript (Ps-ACS1a) and lacks the first 383 bases. Thus, Ps-ACS1b does not encode a full-length ACC synthase protein. Because the Ps-ACS1b sequence is identical to that of Ps-ACS1a, including proper splicing of the second intron, Ps-ACS1b appears to result from the use of an alternative, internal promoter.
Michigan State University-Department of Energy Plant Research Laboratory, East Lansing 48824-1312, USA.
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D017398:Alternative Splicing; D000595:Amino Acid Sequence; D001483:Base Sequence; D003001:Cloning, Molecular; D017124:Conserved Sequence; D019281:Dimerization; D007438:Introns; D008190:Lyases / Q000096:biosynthesis* / Q000737:chemistry / Q000235:genetics*; D008969:Molecular Sequence Data; D008970:Molecular Weight; D011401:Promoter Regions, Genetic; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry; D014158:Transcription, Genetic
D011994:Recombinant Proteins; D008190:Lyases; C021773:1-aminocyclopropanecarboxylate synthase