Muchhal U S, Schwartzbach S D
School of Biological Sciences, University of Nebraska, Lincoln 68588.
Plant Mol Biol. 1992 Jan;18(2):287-99. doi: 10.1007/BF00034956.
A 7.4 kb segment of a Euglena nuclear gene encoding a portion of the polyprotein precursor to the light-harvesting chlorophyll a/b-binding protein of photosystem II (LHCPII) has been isolated and sequenced. Nine exons can be assembled into a continuous open reading frame encoding 113 amino acids of the C-terminus of an LHCPII, followed by 4 complete LHCPIIs. The intron-exon junctions required to maintain maximum amino acid sequence homology between the LHCPIIs encoded by the Euglena genomic clone and Arabidopsis LHCPII do not conform to the consensus splice site sequences present in most eukaryotic organisms. Three types of LHCPIIs are contained within the polyprotein precursor. There is greater than 90% sequence identity at both the protein and nucleic acid level within a type while between types, there is less than 65% sequence identity. All Euglena LHCPIIs contain three hydrophobic membrane-spanning domains in the same positions as found in other LHCPIIs. Hybridization of genomic Southern blots with a probe encoding LHCPII suggests that the Euglena genome encodes a large number (30-50) of LHCPIIs. A probe derived from the 3' end of the sequenced genomic clone hybridizes with equal intensity to 2-3 genomic fragments on Southern blots. The probe encoding LHCPII hybridizes to RNAs of 9.5 and 6.6 kb on northern blots of total RNA while the 3'-end probe hybridizes only to the 6.6 kb RNA. The 6.6 kb LHCPII band detected on northern blots appears to be composed of transcription products derived from 2-3 LHCPII genes. Euglena appears to be unique in that a large number of LHCPIIs are encoded by a small number (3-5) of polyprotein genes.
已分离并测序了眼虫核基因的一段7.4 kb片段，该基因编码光系统II（LHCPII）的捕光叶绿素a/b结合蛋白多蛋白前体的一部分。九个外显子可组装成一个连续的开放阅读框，编码LHCPII C末端的113个氨基酸，随后是4个完整的LHCPII。眼虫基因组克隆编码的LHCPII与拟南芥LHCPII之间保持最大氨基酸序列同源性所需的内含子-外显子连接不符合大多数真核生物中存在的共有剪接位点序列。多蛋白前体中包含三种类型的LHCPII。同一类型内蛋白质和核酸水平的序列同一性均大于90%，而不同类型之间的序列同一性小于65%。所有眼虫LHCPII在与其他LHCPII相同的位置都含有三个疏水跨膜结构域。用编码LHCPII的探针进行基因组Southern杂交表明，眼虫基因组编码大量（30-50个）LHCPII。从测序的基因组克隆3'末端衍生的探针在Southern杂交中与2-3个基因组片段以相同强度杂交。编码LHCPII的探针在总RNA的Northern杂交中与9.5 kb和6.6 kb的RNA杂交，而3'末端探针仅与6.6 kb的RNA杂交。在Northern杂交中检测到的6.6 kb LHCPII条带似乎由2-3个LHCPII基因的转录产物组成。眼虫似乎很独特，因为大量的LHCPII由少数（3-5个）多蛋白基因编码。
