Determination of the lambda prophage gene order in lysogens by deletion mapping exposed an anomaly. The order is a particular circular permutation of the order found by recombination frequencies between genes for vegetatively growing lambda (Fig. 1). On the basis of a small number of genetic experiments Campbell proposed a brilliant explanation for the gene order problem and also made several other predictions concerning problems on integration. The Campbell model was that the lambda DNA, which is linear within the virion, circularizes upon entering a cell and then opens its genome at another point as it reciprocally recombines via a site-specific recombination event mediated by a specialized recombination machinery into the chromosome of the host (Fig. 2). A simple notation has developed for the DNA elements involved in integration and excision. The region of the host DNA into which lambda inserts is labeled BOB’. B denotes the left portion of the bacterial sequence into which lambda inserts, O is the crossover point or region of the recombination between phage and chromosomal DNA, and B’ is the right portion of the bacterial sequence. The entire region BOB’ is called attB. Similarly, the phage regions are called POP’ and attP. The products of integration are BOP’, which is also called attL, and POB’, which is called attR. Note that this notation does not prejudice the discussion by assuming that B and P are homologous or that B is the same as B’. In fact, we can predict that the system would not depend on lengthy homologies between BOB’ and POP’ because if it were, the general recombination system could then recombine to insert or excise a phage genome.

Fig1. The gene orders of lambda phage determined for lysogens by deletion mapping and for lytically infected cells.

Fig2. The Campbell model for lambda integration. Linear phage DNA circularizes soon after infection by association of the A and R ends. Integration occurs by means of a site-specific recombination event in the O regions of the phage and bacterial DNA to generate the integrated phage. P and P’, and B and B’ are the phage and bacterial DNA sequences required for this process.

اخر الاخبار

اخبار العتبة العباسية المقدسة

جمعيَّة العميد تعقد اجتماعًا مع الهيأة العُليا لإحياء التراث استعدادًا ليوم اللغة العربية

استعدادًا لزيارة الأربعين العتبة العباسية المقدسة تعزّز خزين المياه في مجمع أبي الفضل العباس (عليه السلام) عبر خزانات بسعة 900م3

الهيأة العليا لإحياء التراث تنهي استعداداتها لعقد مؤتمر الإمام الحسن (عليه السلام) الثاني عشر في النجف

المجمَع العلمي ينظّم محاضرة توعوية لطلبة مشروع الحفظ في بغداد

المزيد

الآخبار الصحية

أخصائية تكشف خطورة عادة "شائعة" في غسل المناشف

دراسة: بيضة واحدة أسبوعيا قد تقي من الإصابة بـ

على عكس الشائع.. هذا هو العدد المثالي للخطوات اليومية !

شهر التوعية بالساركوما... أطباء يحذرون من "السرطان الصامت"

المزيد

الآخبار التكنلوجية

ذكر أم أنثى؟.. دراسة تنسف الاعتقاد الشائع حول جنس المولود

بحجم برج بيزا.. تحذير من كويكب يقترب من الأرض في هذا الموعد

أقصر يوم في تاريخ البشرية.. الموعد قريب ؟!!

مايكروسوفت تحذر شركات وأجهزة حكومية من هجوم "يوم الصفر"

المزيد

مواضيع ذات صلة

Amplification Techniques in Molecular Biology

Characteristics of Nucleic Acids

solation of Integration-Defective Mutants

Simultaneous Deletion of Chromosomal and Lambda DNA

Mapping Integrated Lambda

Expression Patterns of Developmental Genes

Enhancer Traps for Detecting and Cloning Developmental Genes

Cloning Developmental Genes

General Considerations on Signaling

DNA Strand Inheritance and Switching in Fission Yeast

DNA Cleavage at the MAT Locus

Glucose Metabolism