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CXXC5 is a member of the zinc-finger CXXC family that binds to unmethylated CpG dinucleotides. CXXC5 modulates gene expressions resulting in diverse cellular events mediated by distinct signaling pathways. However, the mechanism responsible for CXXC5 expression remains largely unknown. We found here that of the 14 annotated CXXC5 transcripts with distinct 5′ untranslated regions encoding the same protein, transcript variant 2 with the highest expression level among variants represents the main transcript in cell models. The DNA segment in and at the immediate 5′-sequences of the first exon of variant 2 contains a core promoter within which multiple transcription start sites are present. Residing in a region with high G–C nucleotide content and CpG repeats, the core promoter is unmethylated, deficient in nucleosomes, and associated with active RNA polymerase-II. These findings suggest that a CpG island promoter drives CXXC5 expression. Promoter pull-down revealed the association of various transcription factors (TFs) and transcription co-regulatory proteins, as well as proteins involved in histone/chromatin, DNA, and RNA processing with the core promoter. Of the TFs, we verified that ELF1 and MAZ contribute to CXXC5 expression. Moreover, the first exon of variant 2 may contain a G-quadruplex forming region that could modulate CXXC5 expression.

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Understanding the concepts of quantum mechanics has always been a challenge for undergraduate students. This is especially so because many of the introductory (analytically solvable) systems and problems discussed in textbooks are seemingly abstract. Using approximate experimental demonstrations of such systems and problems have been shown to be very helpful in teaching and illustrating the basic concepts of quantum mechanics. One such system is the particle-inside-a-ring system, whose experimental demonstration was achieved 25 years ago in the form of a "quantum corral" of iron atoms arranged in a ring on a copper surface by using scanning tunneling microscopy. However, this system, which can be a very good model to demonstrate the concepts of quantum mechanics, has not been treated in depth in the literature or in quantum-chemistry textbooks from an educational point of view. Here, we examine the particle-inside-a-ring system and its experimental demonstration in order to elucidate the difference between the superposition and statistical-mixture concepts and to provide an explicit description of how experimental data can be related (fitted) to a theoretical model.