CIRCADIAN RHYTHMS - Cyanobacteria - page 303

C HAPTER 6 C HAPTER

CIRCADIAN RHYTHMS

I. EARLY STUDIES 305

II. CHOICE OF EXPERIMENTAL ORGANISM 305

III. CIRCADIAN CLOCK 308

A) The oscillator in Synechococcus
B) Genes that regulate the clock
C) Properties of Kai proteins
D) Interaction between Kai proteins
IV. INPUT PATHWAYS 320

V. OUTPUT PATHWAYS 323

i) Role of light and dark
ii) Cell division and the rhythms
iii) Adaptive fi tness
VI. KAI GENES IN OTHER CYANOBACTERIA 326

VII. ORIGIN AND EVOLUTION OF KAI GENES AND OTHER CLOCK 327

COMPONENTS

The rotation of the earth about its axis relative to Sun causes the formation of day/night cycles with
a regular periodicity. Accordingly, all living organisms adjust to this external clock by choosing their
respective environmental niches. They do so by expressing endogenous rhythms that can measure
the passage of time on an approximate 24 h scale. Hence these rhythms are known as circadian
(circa= approximately; dies= a day) rhythms. The underlying machinery responsible for the circadian
rhythms is known as circadian clock or biological clock that has three important components, i.e.