Activity of two different silencer elements of the chicken lysozyme gene can be compensated by enhancer elements.

Abstract

The chicken lysozyme gene is constitutively expressed in macrophages. Transfection of recombinant genes containing different portions of the lysozyme 5′ upstream region revealed the existence of two negative transcriptional elements within 1 kb upstream of the start sites. Both elements placed upstream or downstream of a heterologous promoter‐gene unit repress transcription independent of their orientation and are therefore called silencer elements, although their repressing activities 3′ of the gene are reduced. One silencer (N‐1.0 kb) at position −1 kb consists of the central region of the chicken middle repetitive sequence element CR1 and can be divided into two functional domains. N‐1.0 kb is active in all cell types tested. The other silencer (N‐0.25 kb) at position −0.25 kb shows reduced activity in primary macrophages. Despite their different specificities, the activity of both silencer elements can be influenced similarly. An inverse linear relationship between the transcriptional activity of the tested constructs and the potential inhibition by the silencer elements was found: weak transcription units can be strongly repressed, whereas strong transcription units can be only weakly repressed. Such a mechanism may help to turn off completely a particular gene in situations or tissues where strong positive regulators are inactive.

Sequence conservation in avian CR1: an interspersed repetitive DNA family evolving under functional constraints.

“…Fig. 5a illustrates schematically the longer emu clones (clones [12][13][14], and their partial DNA sequence is presented in Fig. 5b, again in comparison with the crane and chicken CR1.…”

“…Chromatographic columns containing CR1 DNA were used to isolate specific nuclear proteins from chicken oviduct tissue, and the fractionated proteins were found to bind at a 3' region of the CR1 sequence (13). Second, in dissecting the upstream region of the chicken lysozyme gene, Baniahamad et al (14) used a reporter gene to define a silencer element in the central portion of a CR1 member found here.…”

Characterization of a silencer element in the first exon of the human osteocalcin gene

“…Similarly, construct pOCATml-6, in which the ATG codon was mutated to AAG, had no change in activity (Table 3). Thus neither of these explanations for silencing activity are (2). Interestingly, this sequence is absent from the human osteocalcin gene (Fig.…”

Negative regulation of the major histocompatibility complex class I promoter in embryonal carcinoma cells.

“…Sci. USA 88 (1991) (36) noted that the NRE described here is similar in sequence to the silencer elements of the lysozyme gene and other genes. However, down-regulation of MHC class I genes probably results from more than one mechanism: a sequence further upstream and distinct from the NRE has been shown to control repression of MHC class I gene expression in cells transformed by the oncogenic adenovirus 12 (37).…”