Cyclins: wheels within wheels.

نویسنده

  • J Pines
چکیده

Cycimns were originally defined as proteins which are synthesized in each cell cycle and destroyed at every mitosis. Cyclins were discovered by T. Hunt and students at the Marine Biological Laboratory, Woods Hole, MA, duningthe 1982 Physiology Course (1). They labeled eggs ofthe sea urchin Arbacia punctulata with [35S]methionine after fertilization and analyzed the temporal pattern of protein synthesis on a i-D SDS2-gel. Sea urchin eggs divide very rapidly and synchronously after fertilization, and Hunt noticed that one protein of ‘ -55 kDa was very strongly labeled after fertilization but appeared to be precipitously destroyed once in each cell cycle, at about the time the egg divided. He named this protein cyciin. By the criterion of synthesis in interphase and destruction at mitosis, cyclins were also identified by Hunt and colleagues in a second sea urchin, Lytechinus pictus, and in the clam Spisula so/idissima (1). Interestingly, in these organisms there appeared to be two cycIins of slightly different molecular mass, which subsequently came to be called Aand B-type cycimns. Aand B-type cyclmns have been cloned from various organisms and are related to one another in the central portion (approximately onethird) of the protein, which has been termed the cyclmn box (2). There are conserved motifs within the cyclmn box which in turn are used to classify the proteins as either A-type on B-type (Fig. 1). in addition, another class of cyciins has since been isolated from budding yeast, as genes which affect the size at which a cell divides and as suppressors of a mutant form of the cell division cycle gene, CDC28 (3-5). These cycimns are only distantly related to other cyciins on the basis of sequence homology, and they appear to have a role in a completely different pant of the cell cycle, G1 phase (6; reviewed in Ref. 7). The common element between the mitotic cyclmns and the G1 cyclins, accounting for their structural homology, is probably that they both bind the protein kinase encoded by the cdc2/ CDC28 gene. The cdc2 gene was isolated by P. Nurse as a cell division cycle mutant in the fission yeast Schizosaccharomyces pombe (8) and shown to encode a 34 kDa protein with all the hallmarks of a protein kinase (9). Nurse found that, at the restrictive temperature, a cdc2 mutant would arrest at two points in the cell cycle: at START in G1 phase before commitment to DNA replication, and in G2

برای دانلود متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید

ثبت نام

اگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید

منابع مشابه

Cyclin specificity: how many wheels do you need on a unicycle?

Cyclin-dependent kinase (CDK) activity is essential for eukaryotic cell cycle events. Multiple cyclins activate CDKs in all eukaryotes, but it is unclear whether multiple cyclins are really required for cell cycle progression. It has been argued that cyclins may predominantly act as simple enzymatic activators of CDKs; in opposition to this idea, it has been argued that cyclins might target the...

متن کامل

Electric Differential for an Electric Vehicle with Four Independent Driven Motors and Four Wheels Steering Ability Using Improved Fictitious Master Synchronization Strategy

Using an Electric Differential (ED) in electric vehicle has many advantages such as flexibility and direct torque control of the wheels during cornering and risky maneuvers. Despite its reported successes and advantages, the ED has several problems limits its applicability, for instance, an increment of control loops and an increase of computational effort. In this paper, an electric differenti...

متن کامل

Kinematic Model of Wheeled Mobile Robots

This paper deals with the structure of the kinematic models of wheeled mobile robots (WMR). A wheeled mobile robot here considered as a planer rigid body that rides on an arbitrary number of wheels. In this paper it is shown that, for a large class of possible configurations of wheels, five types of configurations can be done namely i) fixed standard wheels, ii) steerable standard wheels, iii) ...

متن کامل

Tutte polynomials of wheels via generating functions

We find an explicit expression of the Tutte polynomial of an $n$-fan. We also find a formula of the Tutte polynomial of an $n$-wheel in terms of the Tutte polynomial of $n$-fans. Finally, we give an alternative expression of the Tutte polynomial of an $n$-wheel and then prove the explicit formula for the Tutte polynomial of an $n$-wheel.

متن کامل

Comparison of wheelchair wheels in terms of vibration and spasticity in people with spinal cord injury.

A wheelchair undergoes vibrations while traveling over obstacles and uneven surfaces, resulting in whole body vibration of the person sitting in the wheelchair. According to clinicians, people with spinal cord injury (SCI) report that vibration evokes spasticity. The relatively new Spinergy wheelchair wheels (Spinergy, Inc; San Diego, California) are claimed to absorb more road shock then conve...

متن کامل

Controlling Omni-directional Wheels of a MSL RoboCup Autonomous Mobile Robot

Grupo de Automação e Robótica, Departamento de Electrónica Industrial, Universidade do Minho, Campus de Azurém, 4800 Guimarães, Portugal [email protected], [email protected], [email protected], [email protected], [email protected] Abstract. Autonomous Mobile Locomotion is of extreme importance in RoboCup robots. Even though in 2050 the robotic team will very like...

متن کامل

ذخیره در منابع من


  با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید

برای دانلود متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید

ثبت نام

اگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید

عنوان ژورنال:
  • Cell growth & differentiation : the molecular biology journal of the American Association for Cancer Research

دوره 2 6  شماره 

صفحات  -

تاریخ انتشار 1991