bims-replis Biomed News
on Replisome
Issue of 2025–05–18
two papers selected by
Anna Zawada, International Centre for Translational Eye Research



  1. Front Microbiol. 2025 ;16 1584664
      Replication fork speed (RFS) in Escherichia coli has long been considered constant throughout the replication and cell cycles. In wild-type cells, the circular chromosome is duplicated bidirectionally from oriC, yielding two replication forks that converge at the ter region. Under slow-growth conditions, cells are smaller at initiation than at termination, so DNA replication consumes a larger fraction of cellular resources early in the cell cycle. To challenge this paradigm, we analyzed an E. coli strain with an additional ectopic copy of oriC-designated oriX-inserted midway along the left replichore. In this mutant, replication initiates simultaneously from both oriC and oriX, resulting in four active replication forks early in the cycle. Specifically, the rightward-moving fork from oriX and the leftward-moving fork from oriC converge first, while the leftward-moving fork from oriX is halted at the terA site until the arrival of the rightward-moving oriC fork. Consequently, the number of active replication forks varies dynamically-from zero to four, then two, then one, and finally zero-compared to the fixed zero-two-zero pattern observed in wild-type cells. RFS was calculated using marker frequency analysis of deep sequencing data. Our analysis revealed that RFS is reduced by approximately one third when four replication forks are active and increases by about one fourth when only one fork is active, resulting in a 2-fold variation in RFS during the replication cycle. Moreover, delaying replication initiation or increasing the available dNTP pool normalized these variations, indicating that nucleotide supply is the primary constraint on replication speed. These findings demonstrate that RFS is not inherently constant within a replication cycle and provide a basis for further studies into the factors that regulate replication kinetics.
    Keywords:  DNA replication; DnaA; cell cycle; dNTP pool; marker frequency analysis; oriC; replication fork speed
    DOI:  https://doi.org/10.3389/fmicb.2025.1584664
  2. Eur J Dent. 2025 May 15.
       OBJECTIVE:  Ameloblastoma, though classified as a benign tumor, can induce deformities and functional abnormalities in the craniofacial region. Ki-67 is a typical marker for cell proliferation, with its expression peaking the M phase of the cell cycle or mitosis, indicating active cell division. Cells with high levels of Ki-67 expression are typically in a state of active proliferation. In addition, proliferating cell nuclear antigen (PCNA), a nuclear protein, plays a role in regulating the cell cycle and is involved in deoxyribonucleic acid (DNA) replication and repair processes. PCNA acts as a cofactor in DNA replication and repair processes.
    MATERIAL AND METHODS:  This study used 37 postoperative paraffin blocks for ameloblastoma patients in the period of 2015 to 2023. The samples in the inclusion criteria involved 24 samples with ameloblastomas diagnosis. Immunohistochemistries were used to observe the expression of Ki-67 and PCNA.
    RESULTS:  The lowest expression of Ki-67 and PCNA was found in the plexiform subtype, whereas the highest expression values were found in mixed subtype (follicular-plexiform). The Tukey honestly significant difference test indicated a significant difference in Ki-67 expression in mixed subtypes compared to the plexiform and follicular types, with values of 0.001 (p < 0.05), and for PCNA expression was found with significant difference, 0.001 and 0.000 (p < 0.05), in the mixed subtypes, higher compared to the follicular and plexiform type.
    CONCLUSION:  There is a significant difference in the expression values of Ki-67 and PCNA in the follicular subtype when compared to the plexiform subtype. However, no significant difference in values was observed between the follicular type and the mixed type.
    DOI:  https://doi.org/10.1055/s-0044-1791220