Transcriptional characterization of an ?-zein gene cluster in maize

Abstract

A cluster of five alpha-zein subfamily 4 (alpha-zein SF4) genes are present in a 56 kb region of the maize W22 genome. Two types of alpha-zein SF4 genes are in the cluster. One of the genes, termed a type 1 (T1) alpha-zein SF4 gene, contains no early in-frame stop codons. Four of the genes, termed type 2 (T2) alpha-zein SF4 genes, contain one or two early in-frame stop codons. The base sequence of the T1 alpha-zein SF4 gene is similar (> 90%) to the sequences of any of the four T2 alpha-zein SF4 genes. However, their sequences differ markedly at distances greater than -875 bp upstream from the translation initiation codon of the alpha-zein coding region. This region of dissimilarity is well inside the functional 5'-flanking region for the genes since a 1.8 kb transcript is initiated in this region and the sequences of the T2 alpha-zein SF4 genes are similar in this region. Two sizes of mRNA transcripts, 1.8 kb and 0.9 kb, were detected in a gene specific manner for 4 of the 5 genes in this alpha-zein SF4 gene cluster. One of the T2 alpha-zein SF4 genes had only the 0.9 kb transcript. The RNA level for the 0.9 kb transcript of the T1 alpha-zein SF4 gene was 5- to 10-fold higher than the transcript levels of any of the T2 alpha-zein SF4 genes. In each case, the amount of the 0.9 kb transcript detected was at least 5-fold higher than the amount of the 1.8 kb transcript. A cDNA clone with a sequence identical to a T2 alpha-zein SF4 gene was isolated, providing the first direct evidence for the transcription of T2 alpha-zein genes containing early in-frame stop codon(s) in maize endosperm.

Chromatin and DNA Modifications in theOpaque2-Mediated Regulation of Gene Transcription during Maize Endosperm Development

“…The transcription of azs19.B-1-4 and MAc1 was endosperm specific and constitutive, respectively, and for both genes it was independent of O2 activity. In agreement with previous observations (Liu and Rubenstein, 1993;Song and Messing, 2003), we detected transcripts corresponding to azs22.5, azs22.12, and azs22.11 pseudogenes in wild-type endosperms, while their accumulation was abolished in the o2 mutant. Nevertheless, the comparison of transcript levels of O2 targets after the standardization of qRT-PCR results for primer amplification efficiency indicated that the mRNA amount of azs22 pseudogenes was very low (at least 40 times less compared with the azs22 genes; Figure 1B).…”

Amplicons of maize zein genes are conserved within genic but expanded and constricted in intergenic regions

“…Even the truncated azs22;3 has an intact O2-box. Liu and Rubenstein (1993) have shown that transcription can occur at 22-kDa zein genes with a premature stop codon. However, transcripts accumulate at five-to 10-fold lower levels than from genes with full length open reading frames.…”

Synergy of Two Reference Genomes for the Grass Family

“…One mechanism of gene silencing appears to be the introduction of premature stop codons ). It appears that those genes can still be transcribed, but their mRNAs accumulate at a very reduced level (Liu and Rubenstein, 1993;Song and Messing, 2003). It has been suggested that premature termination of translation triggers accelerated turnover of mRNA (van Hoof and Green, 1996).…”