Homo sapiens L. (human) [HSA]

FULL NAME: DNA primase small subunit


DESCRIPTION:
DNA primase is the polymerase that synthesizes small RNA primers for the Okazaki fragments made during discontinuous DNA replication.
Initiation of nucleic acid synthesis during replication presents a unique challenge to the cell, as DNA polymerases can only extend the 3′-end of an existing DNA chain, but cannot initiate synthesis de novo. A specialized DNA-dependent RNA polymerase, termed primase, is responsible for synthesizing the short RNA primers that are utilised by the replicative DNA polymerases. The antiparallel arrangement of the strands in the DNA double helix means that initiation events must take place repeatedly on the lagging strand, to prime synthesis of each Okazaki fragment. Indeed, the enzymatic activity of the primase is constantly required at the replication fork.
Primases synthesise oligoribonucleotides that are 7–12 nt in length. In the absence of DNA polymerase, primases can extend the primer by multiple rounds of unit-length elongation. Prior to ligation of a newly synthesized Okazaki fragment to the nascent DNA chain, the RNA primer is normally removed.

In bacteria, the primase is a single polypeptide whereas in archaea and eukaryotes the primase is a heterodimeric enzyme comprised of a small subunit PriS endowed with catalytic activity and a large subunit PriL with multiple regulatory functions. The conserved C-terminal sequence of PriL (PriL-CTD) is an iron–sulfur cluster domain with an important functional role in RNA primer synthesis. In eukaryotes the primase is found tightly associated with Pol α and its B subunit in a heterotetrameric complex, the Pol α/primase complex or primosome.

Once the RNA primer has reached its full size, the primase must hand it over to the DNA polymerase for processive elongation. In eukaryotic replication, the hand-off between primase and polymerase takes place within the primosome: the 3′-end of the RNA primer is transferred intramolecularly to the active site of Pol α for limited extension with dNTP. The resulting RNA–DNA primer is then handed over to Pol δ and Pol ε on the lagging and leading strand, respectively, in a process that requires the clamp loader Replication Factor C and the sliding clamp PCNA.


MISCELLANEOUS:
The bound zinc ion is not a cofactor. It is bound to a zinc knuckle motif that may be involved in sequence recognition and the binding of ssDNA (By similarity).


STRUCTURE SIMILARITY:
Belongs to the eukaryotic-type primase small subunit family.


SUBUNIT STRUCTURE:
Heterodimer of a small subunit and a large subunit.


RELATED PATHWAY(S):
DNA replication


Amino acids sequence

        10         20         30         40         50         60
METFDPTELP ELLKLYYRRL FPYSQYYRWL NYGGVIKNYF QHREFSFTLK DDIYIRYQSF
        70         80         90        100        110        120
NNQSDLEKEM QKMNPYKIDI GAVYSHRPNQ HNTVKLGAFQ AQEKELVFDI DMTDYDDVRR
       130        140        150        160        170        180
CCSSADICPK CWTLMTMAIR IIDRALKEDF GFKHRLWVYS GRRGVHCWVC DESVRKLSSA
       190        200        210        220        230        240
VRSGIVEYLS LVKGGQDVKK KVHLSEKIHP FIRKSINIIK KYFEEYALVN QDILENKESW
       250        260        270        280        290        300
DKILALVPET IHDELQQSFQ KSHNSLQRWE HLKKVASRYQ NNIKNDKYGP WLEWEIMLQY
       310        320        330        340        350        360
CFPRLDINVS KGINHLLKSP FSVHPKTGRI SVPIDLQKVD QFDPFTVPTI SFICRELDAI
       370        380        390        400        410        420
STNEEEKEEN EAESDVKHRT RDYKKTSLAP YVKVFEHFLE NLDKSRKGEL LKKSDLQKDF

Encoded by PRIM1 gene

FULL NAME: primase, DNA, polypeptide 1 (49kDa)


OTHER NAME(S):
MGC12308
p49


DESCRIPTION:
The replication of DNA in eukaryotic cells is carried out by a complex chromosomal replication apparatus, in which DNA polymerase alpha and primase are two key enzymatic components. Primase, which is a heterodimer of a small subunit and a large subunit, synthesizes small RNA primers for the Okazaki fragments made during discontinuous DNA replication. The protein encoded by this gene is the small, 49 kDa primase subunit. [provided by RefSeq, Jul 2008]


Nucleic acid sequence

        10         20         30         40         50         60
atggagacgt ttgaccccac cgagctgccc gagctgctta aactttatta ccggaggctc
        70         80         90        100        110        120
tttccctact ctcagtacta tcgctggctc aactacggtg gagtgataaa gaattacttt
       130        140        150        160        170        180
caacaccgtg aattttcatt cacattgaaa gatgatattt acattcgcta ccaatccttc
       190        200        210        220        230        240
aacaaccaga gtgatctgga aaaggagatg cagaaaatga atccatacaa gattgatata
       250        260        270        280        290        300
ggcgcagtat attctcacag acccaatcaa cacaatacag tgaagctggg agctttccag
       310        320        330        340        350        360
gctcaggaaa aagaactggt atttgacatt gacatgacag actatgacga tgtgaggaga
       370        380        390        400        410        420
tgttgtagtt ctgcagacat atgtcctaag tgctggaccc tcatgacaat ggccatacgc
       430        440        450        460        470        480
atcattgaca gagcattgaa ggaggacttt ggatttaagc atcgtctctg ggtatattct
       490        500        510        520        530        540
ggaaggagag gtgttcattg ttgggtctgt gatgaatcag ttagaaaact gtcttctgca
       550        560        570        580        590        600
gtacgttctg ggatagttga gtatttgagc cttgtaaagg gtggtcaaga cgttaaaaag
       610        620        630        640        650        660
aaagttcacc taagtgaaaa aattcaccct tttatcagaa aatctataaa cataataaaa
       670        680        690        700        710        720
aaatactttg aagaatatgc cttggttaat caagatattc tcgaaaataa agaaagctgg
       730        740        750        760        770        780
gataagattt tagcccttgt tcctgaaaca attcatgatg aacttcaaca aagcttccaa
       790        800        810        820        830        840
aagtctcaca attcacttca gcgttgggag cacttgaaga aagtagccag cagatatcag
       850        860        870        880        890        900
aataacatca aaaatgacaa atatggaccc tggctggagt gggagattat gctccagtac
       910        920        930        940        950        960
tgttttccac ggctggatat caatgtcagc aaaggaatca atcatctact gaagagccct
       970        980        990       1000       1010       1020
tttagtgttc atcctaaaac aggtcgcata tctgtgccta ttgatttgca gaaagtggac
      1030       1040       1050       1060       1070       1080
cagtttgatc catttactgt tccgaccata agcttcatct gccgtgaatt ggatgccatt
      1090       1100       1110       1120       1130       1140
tccactaatg aagaggaaaa agaggagaat gaagctgaat ctgatgtcaa acatagaacc
      1150       1160       1170       1180       1190       1200
agagattata agaagaccag tctagcacct tatgtgaaag tttttgaaca ttttcttgaa
      1210       1220       1230       1240       1250       1260
aatctggata aatcccgaaa aggagaactt cttaagaaga gtgatttaca aaaagatttc

tga     

Last modification date: Oct. 22, 2011