Researchers at Northwestern University in the United States have discovered a new repetitive gene cluster sequence that is only expressed in humans and non-human primates. This is the first elongation factor that repeats itself in the human genome and has unique characteristics of primates. This discovery is a breakthrough in human genomic biology and has broad implications for future research in transcriptional regulation, human evolution, and repetitive DNA sequences. This discovery was published in the latest issue of Scientific Progress. In the past 20 years, the rapid advancement of genome sequencing technology has accelerated the exploration of the genetic structure of various regions of the human genome. The larger regions of the human genome are composed of repetitive DNA sequences, which experts refer to as genetic "dark matter". The development of long read sequencing technology enables scientists to study these long "dark matter" sequences and characterize their roles in genetic diversity and evolution. In the current study, while characterizing an anti-cancer compound in human cell lines, the research team accidentally discovered a set of previously uncharacterized genes encoding the ELOA3 protein. This protein is closely related to the elongation protein A (ELOA) protein. Previously, the role of ELOA protein in regulating RNA polymerase II (RNAP II) transcription has been studied, and RNAP II is an essential process for gene expression. Researchers suggest that generally speaking, a single human protein is encoded by a single gene, and closely related proteins may be encoded by different genes located at different chromosomal positions. However, for ELOA3, the feature of multiple genes located at the same gene locus encoding the same protein makes it an interesting research subject. Further research has found that the ELOA3 gene cluster is unique to both human and non-human primates, and the number of ELOA3 gene repetitions varies among individuals and primate species. These observations indicate that the ELOA3 gene cluster has undergone coevolution and gene homogenization in the studied primate species. Using protein biochemistry techniques, the research team found that ELOA3 and ELOA proteins form a different protein complex that regulates RNAP II transcription through a unique biochemical mechanism. Researchers have stated that ELOA3, as a novel RNAP II elongation factor unique to primates, its discovery not only enhances people's understanding of human genomic biology, but also opens a window for cancer targeted drug design. The dynamic properties of ELOA3 repeat clusters may reflect their unique role in regulating gene expression variability between individuals. (Lai Xin She)