原核型聚球藻 RF-1 品系具有概日韻律,其韻律可利用光/暗或在其生
長容許溫度內做小幅度的升溫或降溫加以建立。 有關此藻之韻律研究以
往以固 氮活性及白
胺酸的吸收作為韻律的指標， 本文分析其蛋白質合成速率， 亦可以

清晰的看出有十餘種蛋白質， 其合成具有韻律性。 其中韻律蛋白 COP23

(Circadian Oscillating Polypeptide 23 kDa) 是位於細胞膜上， 它的
韻律經由轉錄階 層所調控。
COP23 不僅在合成上有韻律， 在量上面亦有韻律的變化。 以光/暗

建立韻律， 回到環境不變的條件， 以 35S-Methionine 短暫標幟其合成
之蛋白， 在第二十二
小時， COP23 會迅速分解， 這是在沒有建立韻律的細胞上所看不

到的， 意味著除合成外， 蛋白質之分解亦可能具韻律性； 若加入蛋白
質合成 抑制劑氯黴
素， 這種現象就不會發生。 我們將此蛋白質的基因序列解讀， 它

含有 28 個胺基酸的引導蛋白序列， 此引導蛋白序列不存在於成熟的
COP23， 說明引導
蛋白在 COP23 被送至膜上時已被切除。 為了瞭解 cop23 基因與其它

具有韻律現象之基因間的關係， 本實驗同時對固氮基因的構造加以分析
， 並將 cop23 和
nif 基因二者的轉錄起始定出。 調控 cop23 的 5' 端長達 1.8K， 包括
兩 組多次重複的序列
(GGCGATCGCC; TTATTAATAA)， 以及含 AT 高於 70% 的序列， 但 cop23
與 nif 之上游基因並無明確的相關性。

The prokaryote Synechococcus RF-1 exhibits circadian rhythms of
nitrogen

fixation and leucine uptake after being entrained in a diurnal
light/dark regimen. The rhythms can also be established by small
temperature changes, in either a raised- or a lowered-
temperature cycle, within the growth permissive range. At the
biochemical level, the synthesis of more than ten of its
polypeptides is known to become entrained to a circadian
oscillating pattern. One of the circadian oscillating
polypeptides, COP23, was found to be located in the membrane and
its rhythmic synthesis rate controlled at the transcription
level. In addition to the protein synthesis rate, the content of
COP23 also exhibited a circadian rhythm. Stability of COP23,
examined by 35S-Methionine pulse labeling, revealed that
it was relatively stable in an arrhythmic culture. However, the
exposure of Synechococcus RF-1 to light/dark regimen induced not
only a circadian synthesis rhythm, but also a
rapid protein degradation of COP23 at a defined period of
time. The induction of rapid protein degradation was prevented
by the presence of chloramphenicol. The gene encoding
the COP23 polypeptide has been cloned and sequenced.
The amino acid sequence derived from the open reading frame
revealed that a signal peptide (28 amino acids) does not appear
to be part of the mature COP23. We also cloned and
sequenced the nifHDK operon which contains 4.5Kb.
Transcription start of cop23 and nifHDK operon were determined
by primer extension. The 5' upstream of cop23 is
1.8Kb. It contains multiple repeats of two palindrome
sequences (GGCGATCGCC; TTATTAATAA) and an AT-rich region.
Comparison of the structure of the upstream of cop23 and nifHDK
does not reveal significant similarity.
The prokaryote Synechococcus RF-1 exhibits circadian rhythms of