Summary

Molecular biology and gene expression regulation examine the molecular organization, function, and interactions of DNA, RNA, and proteins. This collection covers the mechanisms through which genetic information is replicated, transcribed, processed, translated, and regulated, including transcriptional control, RNA metabolism, post-transcriptional regulation, protein synthesis, and molecular signaling.

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RNA Transcription
RNA transcription is the template-directed enzymatic synthesis of an RNA molecule from a defined DNA sequence. It is catalyzed by RNA polymerase, which locally separates the DNA strands, reads the template strand in the 3′→5′ direction, and polymerizes complementary ribonucleoside triphosphates into an RNA chain in the 5′→3′ direction through phosphodiester-bond formation [1][2]. The resulting transcript has a nucleotide sequence complementary to the DNA template and corresponds, apart from uracil replacing thymine, to the coding-strand sequence. The process comprises ordered stages of promoter recognition and initiation, promoter escape, elongation of the nascent RNA, and termination with release of the RNA product and polymerase from the transcription unit [2][3]. Its molecular components include a DNA template containing regulatory and transcribed regions, RNA polymerase, ribonucleoside triphosphate substrates, divalent metal ions in the catalytic center, and accessory factors that direct polymerase recruitment, start-site selection, processivity, pausing, RNA processing, and termination [2][3][4]. In eukaryotes, RNA polymerases I, II, and III synthesize specialized RNA classes through associated transcription machineries, with RNA polymerase II producing precursor messenger RNAs and numerous regulatory non-coding RNAs [3][4].
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  • 24 Oct 2026
Topic Review
CRISPR/Cas9
CRISPR/Cas9 is an RNA-guided DNA-targeting system derived from the type II CRISPR adaptive immune systems of bacteria. Its core components are the Cas9 endonuclease and a guide RNA, which may consist of separate CRISPR RNA (crRNA) and trans-activating crRNA (tracrRNA) molecules or a fused single-guide RNA (sgRNA) [1]. Base pairing between the guide-derived spacer sequence and a complementary DNA protospacer directs Cas9 to a specified genomic or extrachromosomal locus. Target recognition additionally requires a nearby protospacer-adjacent motif (PAM), whose sequence is determined by the particular Cas9 ortholog; for the commonly used Streptococcus pyogenes Cas9, this motif is generally 5′-NGG-3′ [1][2]. After PAM recognition and guide–target hybridization, the HNH and RuvC nuclease domains of Cas9 cleave opposite DNA strands to generate a double-strand break [1][3]. CRISPR/Cas9 therefore denotes the guide-RNA-programmable Cas9 system itself, rather than the broader CRISPR family, which includes mechanistically distinct class 1 and class 2 CRISPR systems and non-Cas9 effector proteins [3].
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  • 24 Oct 2026
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